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  • Jääskeläinen, Marko (Helsingin yliopisto, 2012)
    Retrotransposons are major components of most eukaryotic genomes. They resemble retroviruses except that their lifecycle is limited to within the boundaries of the cell. In this thesis work, the goal was to understand the replication of the BARE1 retrotransposon which belongs to the Class I LTR (Long Terminal Repeat) transposable elements (TEs) of the Copia superfamily. The BARE family constitutes about 2.9% of the barley (Hordeum vulgare L.) genome. We systemically searched Expressed Sequence Tag (EST) databases for transcriptionally active TEs, and found that BARE and LTR -retrotransposons in general are shared and widely active in grasses. We raised antibodies to the BARE1 capsid (GAG), integrase (INT), and reverse-transcriptase-RNaseH (RT-RH) proteins and showed that the BARE1 is expressed as one polyprotein of 150 kDa, processed into a shorter 90 kDa form after cleavage of the RT-RH, and further into mature-sized GAG and INT. These proteins were present in barley almost constitutively; only drought-stress had a positive effect on the levels of the GAG protein. Our results show, for the first time, that pools of retrotransposon polyproteins in plant cells are conserved and abundant enough to be detected immunologically in wide selection of species in the Gramineae. We studied the potential sites for BARE replication in barley by immune and in situ localizations. Both root and shoot apical meristems showed the presence of the BARE proteins, supporting the strategy that newly inserted copies must be carried clonally to the cells giving rise to gametes in order to survive in succeeding generations. Moreover, the cells in phloem companion cells showed localization that suggests the BARE may be able to move within the vasculature of the barley. Density gradients were used to study whether the BARE forms VLPs in barley cells. Fractions positive for BARE1 GAG and INT were visualized in transmission electron microscopy using negative staining. This was the first time VLPs were demonstrated in any plant. The VLP assembly requires excess amounts of GAG, whereas the BARE1 encodes its proteins in a single open reading frame. We observed three different pools of RNA transcripts, one for the polyprotein translation, one for encapsidation and reverse transcription, and a third one that is spliced so that it can translate only GAG, thus contributing to a comparatively larger pool of GAG. The transcript dedicated for encapsidation lacks both the cap and poly(A) for translatability, but contains the R regions critical for replication into the complementary DNA that can be inserted back into the host genome. Evidence for these new BARE insertions was found by comparing polymorphism revealed by PCR methods between several grass species. Taken together, we found that the BARE elements are capable to accomplish their lifecycle not only in barley, but in grass species in general, and thus contribute to the growth of their genome sizes.
  • Uusitalo, Matti (Helsingin yliopisto, 2010)
    The thesis provides a proposal to divide Alycidae G. Canestrini & Fanzago into two subfamilies and four tribes. This new hierarchy is based on a reassessment and reranking of new and previously known synapomorphies of the clusters concerned by cladistic analysis, using 60 morphological characters for 48 ingroup species. The basic characters of the taxa are illustrated either by SEM micrographs (Scanning Electron Microscopy) or by outline drawings. The presented classification includes the definitions of Alycini G. Canestrini & Fanzago new rank; Bimichaeliini Womersley new rank; Petralycini new rank; and the (re)descriptions of Alycus C.L. Koch, Pachygnathus Dugès, Amphialycus Zachvatkin, Bimichaelia Thor and Laminamichaelia gen. nov. The species described or redescribed are: Pachygnathus wasastjernae sp. nov. from Kvarken (Merenkurkku), Finland; Pachygnathus villosus Dugès (in Oken); Alycus roseus C.L. Koch; Alycus denasutus (Grandjean) comb. and stat. nov.; Alycus trichotus (Grandjean) comb. nov.; Alycus marinus (Schuster) comb. nov.; Amphialycus (Amphialycus) pentophthalmus Zachvatkin; Amphialycus (Amphialycus) leucogaster (Grandjean); and Amphialycus (Orthacarus) oblongus (Halbert) comb. nov.; Bimichaelia augustana (Berlese); Bimichaelia sarekensis Trägårdh; Laminamichaelia setigera (Berlese) comb. nov.; Laminamichelia arbusculosa (Grandjean) comb. nov.; Laminamichelia subnuda (Berlese) comb. nov. and Petralycus unicornis Grandjean. Fourteen nominal species were found to be junior synonymies. The importance of sensory organs in taxonomy is well recognized, but inclusion of the elaborate skin pattern seemed to improve essentially the usefulness of the prodorsal sensory area. The detailed pictures of the prodorsa of the European alycids could be used like passport photographs for the species. A database like this of prodorsa of other mite taxa as well might be an answer to future needs of species identification in soil zoology, ecology and conservation.
  • Grönberg, Henrietta (Helsingin yliopisto, 2008)
    Rhizoctonia spp. are ubiquitous soil inhabiting fungi that enter into pathogenic or symbiotic associations with plants. In general Rhizoctonia spp. are regarded as plant pathogenic fungi and many cause root rot and other plant diseases which results in considerable economic losses both in agriculture and forestry. Many Rhizoctonia strains enter into symbiotic mycorrhizal associations with orchids and some hypovirulent strains are promising biocontrol candidates in preventing host plant infection by pathogenic Rhizoctonia strains. This work focuses on uni- and binucleate Rhizoctonia (respectively UNR and BNR) strains belonging to the teleomorphic genus Ceratobasidium, but multinucleate Rhizoctonia (MNR) belonging to teleomorphic genus Thanatephorus and ectomycorrhizal fungal species, such as Suillus bovinus, were also included in DNA probe development work. Strain specific probes were developed to target rDNA ITS (internal transcribed spacer) sequences (ITS1, 5.8S and ITS2) and applied in Southern dot blot and liquid hybridization assays. Liquid hybridization was more sensitive and the size of the hybridized PCR products could be detected simultaneously, but the advantage in Southern hybridization was that sample DNA could be used without additional PCR amplification. The impacts of four Finnish BNR Ceratorhiza sp. strains 251, 266, 268 and 269 were investigated on Scot pine (Pinus sylvestris) seedling growth, and the infection biology and infection levels were microscopically examined following tryphan blue staining of infected roots. All BNR strains enhanced early seedling growth and affected the root architecture, while the infection levels remained low. The fungal infection was restricted to the outer cortical regions of long roots and typical monilioid cells detected with strain 268. The interactions of pathogenic UNR Ceratobasidium bicorne strain 1983-111/1N, and endophytic BNR Ceratorhiza sp. strain 268 were studied in single or dual inoculated Scots pine roots. The fungal infection levels and host defence-gene activity of nine transcripts [phenylalanine ammonia lyase (pal1), silbene synthase (STS), chalcone synthase (CHS), short-root specific peroxidase (Psyp1), antimicrobial peptide gene (Sp-AMP), rapidly elicited defence-related gene (PsACRE), germin-like protein (PsGER1), CuZn- superoxide dismutase (SOD), and dehydrin-like protein (dhy-like)] were measured from differentially treated and un-treated control roots by quantitative real time PCR (qRT-PCR). The infection level of pathogenic UNR was restricted in BNR- pre-inoculated Scots pine roots, while UNR was more competitive in simultaneous dual infection. The STS transcript was highly up-regulated in all treated roots, while CHS, pal1, and Psyp1 transcripts were more moderately activated. No significant activity of Sp-AMP, PsACRE, PsGER1, SOD, or dhy-like transcripts were detected compared to control roots. The integrated experiments presented, provide tools to assist in the future detection of these fungi in the environment and to understand the host infection biology and defence, and relationships between these interacting fungi in roots and soils. This study further confirms the complexity of the Rhizoctonia group both phylogenetically and in their infection biology and plant host specificity. The knowledge obtained could be applied in integrated forestry nursery management programmes.
  • Kupiainen, Kaarle (Helsingin yliopisto, 2007)
    Vehicles affect the concentrations of ambient airborne particles through exhaust emissions, but particles are also formed in the mechanical processes in the tire-road interface, brakes, and engine. Particles deposited on or in the vicinity of the road may be re-entrained, or resuspended, into air through vehicle-induced turbulence and shearing stress of the tires. A commonly used term for these particles is road dust . The processes affecting road dust emissions are complex and currently not well known. Road dust has been acknowledged as a dominant source of PM10 especially during spring in the sub-arctic urban areas, e.g. in Scandinavia, Finland, North America and Japan. The high proportion of road dust in sub-arctic regions of the world has been linked to the snowy winter conditions that make it necessary to use traction control methods. Traction control methods include dispersion of traction sand, melting of ice with brine solutions, and equipping the tires with either metal studs (studded winter tires), snow chains, or special tire design (friction tires). Several of these methods enhance the formation of mineral particles from pavement wear and/or from traction sand that accumulate in the road environment during winter. When snow and ice melt and surfaces dry out, traffic-induced turbulence makes some of the particles airborne. A general aim of this study was to study processes and factors underlying and affecting the formation and emissions of road dust from paved road surfaces. Special emphasis was placed on studying particle formation and sources during tire road interaction, especially when different applications of traction control, namely traction sanding and/or winter tires were in use. Respirable particles with aerodynamic diameter below 10 micrometers (PM10) have been the main concern, but other size ranges and particle size distributions were also studied. The following specific research questions were addressed: i) How do traction sanding and physical properties of the traction sand aggregate affect formation of road dust? ii) How do studded tires affect the formation of road dust when compared with friction tires? iii) What are the composition and sources of airborne road dust in a road simulator and during a springtime road dust episode in Finland? iv) What is the size distribution of abrasion particles from tire-road interaction? The studies were conducted both in a road simulator and in field conditions. The test results from the road simulator showed that traction sanding increased road dust emissions, and that the effect became more dominant with increasing sand load. A high percentage of fine-grained anti-skid aggregate of overall grading increased the PM10 concentrations. Anti-skid aggregate with poor resistance to fragmentation resulted in higher PM levels compared with the other aggregates, and the effect became more significant with higher aggregate loads. Glaciofluvial aggregates tended to cause higher particle concentrations than crushed rocks with good fragmentation resistance. Comparison of tire types showed that studded tires result in higher formation of PM emissions compared with friction tires. The same trend between the tires was present in the tests with and without anti-skid aggregate. This finding applies to test conditions of the road simulator with negligible resuspension. Source and composition analysis showed that the particles in the road simulator were mainly minerals and originated from both traction sand and pavement aggregates. A clear contribution of particles from anti-skid aggregate to ambient PM and dust deposition was also observed in urban conditions. The road simulator results showed that the interaction between tires, anti-skid aggregate and road surface is important in dust production and the relative contributions of these sources depend on their properties. Traction sand grains are fragmented into smaller particles under the tires, but they also wear the pavement aggregate. Therefore particles from both aggregates are observed. The mass size distribution of traction sand and pavement wear particles was mainly coarse, but fine and submicron particles were also present.
  • Molotkov, Dmitry (Helsingin yliopisto, 2014)
    Among other glial cell types such as microglia, oligodendrocytes and radial glia, astrocytes are known to be involved in brain function; metabolically supporting neurons, regulating blood flow dynamics, participating in the development of pathological states, sensing and modulating synaptic activity. At the same time the complex astrocytic morphology, with a number of highly ramified peripheral processes located near the synaptic terminals, suggests them as a possible source for morpho-functional plasticity in the brain. This thesis summarizes the work on the in vitro development and further in vivo implementation, using a gene delivery system, of a tool for suppressing activity-dependent astrocytic motility. Calciuminduced astrocyte process outgrowth and its dependence on Profilin-1, novel in vivo gene delivery approaches, a demonstration of astrocytic motility in vivo and the independence of visual processing from astrocytic motility rates are the main findings of the project. The results described in this work increase our understanding of the interactions occurring between astrocytes and neurons as well as the consequences for brain function.
  • Mantela, Johanna (Helsingin yliopisto, 2010)
    The inner ear originates from an ectodermal thickening called the otic placode. The otic placode invaginates and closes to an otic vesicle, the otocyst. The otocyst epithelium undergoes morphogenetic changes and cell differentiation, leading to the formation of the labyrinth-like mature inner ear. Epithelial-mesenchymal interactions control inner ear morphogenesis, but the modes and molecules are largely unresolved. The expressions of negative cell cycle regulators in the epithelium of the early-developing inner ear have also not been elucidated. The mature inner ear comprises the hearing (cochlea) and balance (vestibular) organs that contain the nonsensory and sensory cells. In mammals, the inner ear sensory cells, called hair cells, exit the cell cycle during embryogenesis and are mitotically quiescent during late-embryonic differentiation stages and postnatally. The mechanisms that maintain this hair cell quiescense are largely unresolved. In this work I examined 1) the epithelial-mesenchymal interactions involved in inner ear morphogenesis, 2) expression of negative cell cycle regulators in the epithelium of the early developing inner ear and 3) the molecular mechanisms that maintain the postmitotic state of inner ear sensory cells. We observed that during otocyst stages, epithelial fibroblast growth factor 9 (Fgf9) communicates with the surrounding mesenchyme, where its receptors are expressed. Fgf9 inactivation leads to reduced proliferation of the surrounding vestibular mesenchyme and to the absence of semicircular canals. Semicircular canal development is blocked, since fusion plates do not form. These results show that the mesenchyme directs fusion plate formation and give direct evidence for the existence of reciprocal epithelial-mesenchymal interactions in the developing inner ear. Cyclin-dependent kinase inhibitors (CKIs) are negative regulators of proliferation. We show that the members of the Cip/Kip family of CKIs (p21Cip1, p27Kip1 and p57Kip2) are expressed in the early-developing inner ear. Our expression data suggest that CKIs divide the otic epithelium into proliferative and nonproliferative compartments that may underlie shaping of the otocyst. At later stages, CKIs regulate proliferation of the vestibular appendages, and this may regulate their continual growth. In addition to restricting proliferation, CKIs may play a role in regional differentiation of various epithelial cells. Differentiating and adult inner ear hair cells are postmitotic and do not proliferate in response to serum or mitogenic growth factors. In our study, we show that this is the result of the activity of negative cell cycle regulators. Based on expression profiles, we first focused on the retinoblastoma (Rb) gene, which functions downstream of the CKIs. Analysis of the inner ear phenotype of Rb mutant mice show, that the retinoblastoma protein regulates the postmitotic state of hair cells. Rb inactivation leads to hyperplasia of vestibular and cochlear sensory epithelia that is a result of abnormal cell cycle entry of differentiated hair cells and of delayed cell cycle exit of the hair cell precursor cells. In addition, we show that p21Cip1 and p19Ink4d cooperate in maintaining the postmitotic state of postnatal auditory hair cells. Whereas inactivation of p19Ink4d alone leads to low-level S-phase entry (Chen et al., 2003) and p21Cip1 null mutant mice have a normal inner ear phenotype, codeletion of p19Ink4d and p21Cip1 triggers high-level S-phase entry of auditory hair cells during early postnatal life, which leads to supernumerary hair cells. The ectopic hair cells undergo apoptosis in all of the mutant mice studied, DNA damage being the immediate cause of this death. These findings demonstrate that the maintenance of the postmitotic state of hair cells is regulated by Rb and several CKIs, and that these cell cycle regulators are critical for the lifelong survival of hair cells. These data have implications for the future design of therapies to induce hair cell regrowth.
  • Pummila, Marja (Helsingin yliopisto, 2009)
    Several organs of the embryo develop as appendages of the ectoderm, the outermost layer of the embryo. These organs include hair follicles, teeth and mammary glands, which all develop as a result of reciprocal tissue interactions between the surface epithelium and the underlying mesenchyme. Several signalling molecules regulate ectodermal organogenesis the most important ones being Wnts, fi broblast growth factors (Fgfs), transforming growth factor -βs (Tgf-βs) including bone morphogenetic proteins (Bmps), hedgehogs (Hhs), and tumour necrosis factors (Tnfs). This study focuses on ectodysplasin (EDA), a signalling molecule of the TNF superfamily. The effects of EDA are mediated by its receptor EDAR, an intracellular adapter protein EDARADD, and downstream activation of the transcription factor nuclear factor kappa-B (NF-кB). Mice deficient in Eda (Tabby mice), its receptor Edar (downless mice) or Edaradd (crinkled mice) show identical phenotypes characterised by defective ectodermal organ development. These mouse mutants serve as models for the human syndrome named hypohidrotic ectodermal dysplasia (HED) that is caused by mutations either in Eda, Edar or Edaradd. The purpose of this study was to characterize the ectodermal organ phenotype of transgenic mice overexpressing of Eda (K14-Eda mice), to study the role of Eda in ectodermal organogenesis using both in vivo and in vitro approaches, and to analyze the potential redundancy between the Eda pathway and other Tnf pathways. The results suggest that Eda plays a role during several stages of ectodermal organ development from initiation to differentiation. Eda signalling was shown to regulate the initiation of skin appendage development by promoting appendageal cell fate at the expense of epidermal cell fate. These effects of Eda were shown to be mediated, at least in part, through the transcriptional regulation of genes that antagonized Bmp signalling and stimulated Shh signalling. It was also shown that Eda/Edar signalling functions redundantly with Troy, which encodes a related TNF receptor, during hair development. This work has revealed several novel aspects of the function of the Eda pathway in hair and tooth development, and also suggests a previously unrecognized role for Eda in mammary gland development.
  • Rouhiainen, Ari (Helsingin yliopisto, 2008)
    The matrix of blood is a liquid plasma that transports molecules and blood cells within vessels lined by endothelial cells. High-mobility group B1 (HMGB1) is a protein expressed in blood cells. Under normal circumstances, HMGB1 is virtually absent from plasma, but during inflammation or trauma its level in plasma is increased. In resting and quiescent cells, HMGB1 is usually localized in the intracellular compartment, with the exception of motile cells that express HMGB1 on their outer surface to mediate cell migration. During cell transformation or immune cell activation HMGB1 can be actively secreted outside of the cell. Further, when a cell is damaged, HMGB1 can passively leak into extracellular environment. Extracellular HMGB1 can then participate in regulation of the immune response and under some conditions it can mediate lethality in systemic inflammatory response. The aim of this study was to evaluate the expression and functions of HMGB1 in cells of the vascular system and to investigate the prognostic value of circulating HMGB1 in severe sepsis and septic shock. HMGB1 was detected in platelets, leukocytes, and endothelial cells. HMGB1 was released from platelets and leukocytes, and it was found to mediate their adhesive and migratory functions. During severe infections the plasma levels of HMGB1 were elevated; however, no direct correlation with lethality was found. Further, the analysis of proinflammatory mechanisms suggested that HMGB1 forms complexes with other molecules to activate the immune system. In conclusion, HMGB1 is expressed in the cells of the vascular system, and it participates in inflammatory mechanisms by activating platelets and leukocytes and by mediating monocyte migration.
  • Strengell, Mari (Helsingin yliopisto, 2005)
  • Huttunen, Henri (Helsingin yliopisto, 2002)
  • Koski-Vähälä, Jukka (Helsingin yliopisto, 2001)
  • Lappalainen, Hanna (Helsingin yliopisto, 2010)
    In northern latitudes, temperature is the key factor driving the temporal scales of biological activity, namely the length of the growing season and the seasonal efficiency of photosynthesis. The formation of atmospheric concentrations of biogenic volatile organic compounds (BVOCs) are linked to the intensity of biological activity. However, interdisciplinary knowledge of the role of temperature in the biological processes related to the annual cycle and photosynthesis and atmospheric chemistry is not fully understood. The aim of this study was to improve understanding of the role of temperature in these three interlinked areas: 1) onset of growing season, 2) photosynthetic efficiency and 3) BVOC air concentrations in a boreal forest. The results present a cross-section of the role of temperature on different spatial (southern northern boreal), structural (tree forest stand - forest) and temporal (day-season- year) scales. The fundamental status of the Thermal Time model in predicting the onset of spring recovery was confirmed. However, it was recommended that sequential models would be more appropriate tools when the onset of the growing season is estimated under a warmer climate. A similar type of relationship between photosynthetic efficiency and temperature history was found in both southern and northern boreal forest stands. This result draws attention to the critical question of the seasonal efficiency of coniferous species to emit organic compounds under a warmer climate. New knowledge about the temperature dependence of the concentrations of biogenic volatile organic compounds in a boreal forest stand was obtained. The seasonal progress and the inter-correlation of BVOC concentrations in ambient air indicated a link to biological activity. Temperature was found to be the main driving factor for the concentrations. However, in addition to temperature, other factors may play a significant role here, especially when the peak concentrations are studied. There is strong evidence that the spring recovery and phenological events of many plant species have already advanced in Europe. This study does not fully support this observation. In a boreal forest, changes in the annual cycle, especially the temperature requirement in winter, would have an impact on the atmospheric BVOC composition. According to this study, more joint phenological and BVOC field observations and laboratory experiments are still needed to improve these scenarios.
  • Li, Jing (Helsingin yliopisto, 2014)
    It has been well established that environmentally induced alterations in gene expression are mediated by transcription factors (TFs). One of the important plant-specific TF groups is the WRKY (TFs containing a highly conserved WRKY domain) family, which is involved in regulation of various physiological programs including biotic and abiotic defenses, senescence and trichome development. Two members of WRKY group III in Arabidopsis thaliana, WRKY54 and WRKY70, are demonstrated in this study to be key components in cooperative regulation of developmental senescence, osmotic stress response as well as specific pathogen defenses. As revealed by molecular studies, we found that WRKY54, the closest homologue of WRKY70, exhibited a similar expression pattern as WRKY70 and also functioned in leaf senescence. Disruption of both WRKY54 and WRKY70 resulted in clearly enhanced premature senescence, suggesting that WRKY54 and WRKY70 co-operate as negative regulators of senescence. In addition, yeast two-hybrid analysis showed that WRKY54, WRKY70 and WRKY53 could independently interact with WRKY30. Moreover, the phytohormone salicylic acid (SA) positively affected the expression of WRKY54,WRKY70, WRKY53 and WRKY30. Additionally, WRKY53 and WRKY30 but not WRKY54 and WRKY70 were responsive to reactive oxygen species (ROS) such as hydrogen peroxide (H2O2), a central factor in senescence. All of these data suggest that WRKY54,WRKY70 and WRKY53 act as critical regulators in modulating the process of senescence through independent interaction with WRKY30. The involvement of WRKY54 and WRKY70 in abiotic stress responses was also explored in this study. The transient induction of WRKY54 and WRKY70 by osmotic stress implicated that they might play roles in the abiotic stress response. The wrky54wrky70 double mutant showed enhanced tolerance to osmotic stress compared to the corresponding single mutants and wild-type plants, indicating that these two TFs cooperate as negative regulators of the osmotic stress response. Although the tolerance to osmotic stress was improved in the wrky54wrky70 double mutant, neither the expression of osmotic stress-related genes nor the accumulation of the osmolyte proline was enhanced. The suppressed gene expression in the wrky54wrky70 double mutant is SA dependent,but the osmotic stress tolerance results more directly from the involvement of both negative regulators WRKY54 and WRKY70. In addition, abscisic acid (ABA)signaling was also involved in this suppression. The final analysis showed that the enhanced tolerance in the wrky54wrky70 double mutant was correlated with improved water retention and enhanced stomatal closure. Consequently, the crosstalk between SA mediated biotic and ABA-mediated abiotic stress responses is modulated by WRKY54 and WRKY70. The contribution of both WRKY54 and WRKY70 to plant disease resistance remains unclear although the role of WRKY70 in biotic stress has been previously characterized. Non-stressed wrky54wrky70 double mutant exhibited constitutively expressed defense-related genes and accumulation of H2O2, resulting in pre-formed defense to necrotrophic pathogens such as Pectobacterium carotovorum and Botrytis cinerea. However, this pre-formed resistance was compromised in non-stressed wrky54wrky70sid2-1 triple mutant due to the reduced level of SA. These results suggest that increased SA leads to accumulation of H2O2 which is required to activate antimicrobial defenses to pathogens. Furthermore, genes encoding cell wall-related peroxidases and cell wall modification proteins were up-regulated in the wrky54wrky70 double mutant but not in the wrky54wrky70sid2-1 triple mutant, indicating that the cell wall-associated defense to necrotrophs could result from the elevated SA level in the wrky54wrky70 double mutant. However, this cell wall-associated resistance in wrky54wrky70 did not contribute to the defense against biotrophs. This might require additional defense measures controlled by WRKY54 and WRKY70 which are not activated in the double mutant, although the SA responsive genes are up-regulated by the accumulation of H2O2.
  • Rossi, Jari (Helsingin yliopisto, 2003)
  • Cui, Fuqiang (Hansaprint, 2014)
    To face the constant challenges from numerous pathogens in the environment, sophisticated defense systems have evolved in plants. Reactive oxygen species (ROS) and phytohormones are important cellular compounds that regulate plant defense systems to overcome biotic stresses from different pathogens. Against biotrophic pathogens, which require living host cells, hypersensitive cell death response (HR), a type of programed cell death mediated by ROS and salicylic acid (SA), is effective for immunity. However, to necrotrophic pathogens, which take host cell death as a hallmark of a successful colonization, the roles of ROS and phytohormones in the manipulation of cell death during plant defense are more complex. In this work, we utilized the model necrotrophic pathogen Botrytis cinerea (Botrytis; grey mold) and the model plant Arabidopsis thaliana (Arabidopsis), using mutants in reverse genetic screens, especially radical-induced cell death1 (rcd1) and botrytis susceptible1 (bos1), were used to study the functions of ROS and phytohormones in plant-Botrytis interactions. It was found that Botrytis-triggered signaling in Arabidopsis mostly overlapped with the signaling triggered by apoplastic ROS but not intracellular ROS. However, rcd1 and bos1 exhibited opposite symptoms in response to Botrytis and apoplastic ROS. This suggested that the resistance signaling regulated by RCD1 or BOS1 were distinct from a more common signaling programs induced by Botrytis and apoplastic ROS. Further study revealed that RCD1 negatively regulated Botrytis resistance independent of stress-hormones. RCD1 positively regulated Botrytis-toxin sensitivity and brassinosteroid (BR) signaling, which was demonstrated to negatively regulate plant resistance to Botrytis. In the BOS1 study, suppression of abscisic acid (ABA)-elicited cell death and control of cell death spread were identified as pivotal functions of BOS1 in its regulation of host resistance to Botrytis. This work emphasized the negative roles of both BR and ABA in response to Botrytis infection. Considering the established facts that: 1) ABA promoted plant cell death, 2) BR deficiency leads to delayed senescence, and 3) the ROS burst causes damage to both host and Botrytis; this work supports the view that cell death control plays a pivotal role in plant-Botrytis interactions, where defense combined with less cell death confers plants with an advantage in the battle against Botrytis.