Browsing by Subject "Plant Science"

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  • Zhao, Yafei (Helsingin yliopisto, 2019)
    Flowers and their number and arrangement within inflorescences are essential for the reproductive fitness and adaptive success of plants as well as for human sustenance. Comparative studies using species representing various plant lineages are a prerequisite for a comprehensive understanding of the development of diverse flower forms during the evolution of plants. In addition to a few classical model plants, new models, including core eudicots Asteraceae and basal eudicots Papaveraceae, have emerged to enhance our current understanding of the genetic networks in the regulation of plant growth and development from an evolutionary developmental biology perspective. This thesis seeks to understand the evolutionary origin of the Asteraceae capitulum and the regulatory networks of flower type specification as well as to illustrate the ancestral functions of CYCLOIDEA/TEOSINTE BRANCHED1 (CYC/TB1)-like (CYL) genes in basal eudicots. The Asteraceae inflorescence (capitulum, or flower head) superficially resembles a solitary flower, but it is a tightly packed structure composed of different types of flowers, including marginal ray flowers and central disc flowers. Such evolutionary innovations, as studied in Gerbera hybrida here, are owing to the novel functions of the gerbera orthologues of flower meristem identity (FMI) genes LEAFY (GhLFY) and UNUSUAL FLORAL ORGANS (GhUFO) as well as the regulatory networks involving MADS-box and TCP transcription factors (TFs). The expression domain of GhLFY at the inflorescence meristem mimics that of a single flower meristem, suggesting that the Asteraceae capitulum resembles a solitary flower not only morphologically but also at the molecular level. This expression pattern defines the capitulum as a determinate structure that can display floral fate upon ectopic GhUFO expression. Additionally, suppression of GhLFY and GhUFO led to a loss of FMI and suppressed MADS-box floral organ identity genes in a flower type-dependent manner. In particular, GhLFY regulates the early ontogeny of ray flowers, providing the first molecular evidence for how this structure has evolved. We speculate that the differentiation of flower types in Asteraceae is associated with their independent evolutionary origins from separate branching systems. Furthermore, the establishment of the regulatory networks amongst TCP and MADS-box gene family members in flower type specification provides additional support for distinct genetic origins of flower types. As trans-acting regulators of GhCYC3, the strongest CYC-like TCP gene in specifying ray flower identity, the CINCINNATA (CIN)-like TCP GhCIN1 co-localises with GhCYC3 in ray primordia and specifies the development of ray ligules. Moreover, we discovered that the whorl-specific MADS-box TFs control GhCYC3 expression during flower organ development: SEPALLATA3-like GERBERA REGULATOR OF CAPITULUM DEVELOPMENT5 (GRCD5) specifies ray ligule elongation, and C-class GERBERA AGAMOUS-LIKE1 (GAGA1) controls staminode development in ray flowers. Papaveraceae, belonging to a lineage basal to all other eudicots, represents a phylogenetically important family to understand the origin, evolution, and diversification of CYL genes in eudicots. Comparative studies between Eschscholzia californica and Cysticapnos vesicaria revealed their conserved functional roles in shoot branching, petal size, flower symmetry, and stamen growth, although in a species-specific manner. Nonetheless, our studies revealed a novel function in perianth development for CyveCYLs that were shown to specify the distinction of sepal and petal identity by suppressing B-class genes expression in C. vesicaria. These data indicate that instead of recruiting completely new regulators, the evolution of divergent morphologies employs conserved regulatory genes that show varying spatial/temporal expression patterns to perform their functions within modified regulatory networks, thereby contributing to the morphological diversification and origin of evolutionary innovations.
  • Sun, Yu (Helsingin yliopisto, 2019)
    Fossil evidence suggests that liverworts may have existed already in the Ordovician. The long-standing hypothesis, that widely disjunct geographic ranges of various extant liverwort groups have been largely resulted from vicariance events from fragmentation of widespread ancestors through tectonic plate movements, has been challenged by the recent studies based on molecular data. In this thesis, two groups of the leafy liverworts in the order Jungermanniales were investigated in order to better understand the phylogenetic relationship and biogeography of liverworts. They are the family Schistochilaceae ranging mostly in the Southern Hemisphere, and the cosmopolitan genus Herbertus of family Herbertaceae. Both families possess a diverse morphology and wide disjunct distribution. The phylogeny and biogeographic history of Schistochilaceae and Herbertus were studied by using DNA sequence data of chloroplast and nuclear gene regions. Morphological characters used for species delimitation were also studied and re-evaluated. Schistochilaceae is resolved as monophyletic being one of the early derived leafy liverwort groups. The phylogenetic position of the Chilean endemic Pleurocladopsis simulans is resolved within the genus Schistochila and the new combination Schistochila simulans (C. Massal.) Xiao L. He & Yu Sun is made. Schistochilaceae is inferred to have originated in the Late Cretaceous at c.100 Mya, in an ancestral area including southern South America, West Antarctica and New Zealand. New Zealand was recognized as the early divergence and dispersal center, most dispersals were transoceanic. Herbertus is resolved as a monophyletic group with one clade consisting of the southern hemispheric taxa Herbertus runcinatus, H. oldfieldianus, and H. juniperoideus, and the other including species of H. sendtneri complex and of H. aduncus complex, mostly belonging to the Northern Hemisphere. H. armitanus and H. circinatus were synonymized with H. sendtneri. H. borealis, H. buchii, H. delavayi, H. dicranus, H. kurzii, H. longifissus, H. norenus and H. stramineus were synonymized with H. aduncus. Herbertus is inferred to have originated in the Cenozoic era about 51 Mya, in an ancestral area including southern South America, the Neotropics, Oceania, and Southeast Asia, supporting its Gondwanan origin. In the Southern Hemisphere the distribution pattern of Herbertus is characterized by in situ persistence and did not show further dispersal until the uplift of the Andean Cordillera. Herbertus in the Northern Hemisphere showed more recent diversifications, wide range expansions both north- and southward and repeated recolonizations, and the range shifts had occurred more frequently since the late Miocene. Long-distance dispersal has played an important role in the formation of the global distribution pattern of the genus. Our obtained phylogenies of liverworts all resolved the New Zealand endemic Herzogianthus vaginatus as the first diverged lineage in the Jungermanniales, not supporting its current placement in the Ptilidiales. Our study supports the southern temperate origins for both Schistochilaceae and Herbertus, and most of the diversification occurred in the Cenozoic, a pattern that has been shown to occur also in other leafy liverwort groups. Our results suggest that species with separate sexes do not constrain long-distance dispersal. The causes for the formation of current geographical ranges of liverworts seem to be manifold, likely linked with ecophysiology, lineage age, dispersibility and diversification rate.
  • Hunter, Kerri (Helsingin yliopisto, 2019)
    In order to maintain health, growth, and productivity, plants must be able to adapt to increasingly variable environmental conditions. Plants are continuously flooded with information from their surrounding environment, which must be sensed, incorporated, and responded to accordingly. Much of the communication between plant cells and the extracellular environment is carried out by the receptor-like protein kinases (RLKs), including the cysteine-rich receptor-like kinase (CRK) subfamily. Despite the large size of the CRK gene family, their physiological roles and functions on a biochemical and cellular level remain largely uncharacterized. We performed large scale phenotyping of a crk T-DNA mutant collection in Arabidopsis thaliana (Arabidopsis), which suggested roles for the CRKs in several developmental processes, as well as during abiotic and biotic stress responses. CRK2 emerged as an important CRK, with several strong loss-of-function phenotypes and a notable phylogenetic position. We established that CRK2 enhances salt tolerance through the regulation of callose synthase 1 (CALS1) dependent callose deposition at plasmodesmata. This revealed a previously uncharacterized role for callose deposition in response to high salinity. We showed that this callose deposition has an effect on plasmodesmal permeability, and therefore a potential impact on intercellular signalling. Additionally, CRK2 was found to regulate the formation of an unknown vesicle type during salt stress, which could possibly be involved in cell-to-cell signalling as well. We have described how CRK2 regulates ROS production during immunity by regulation of RBOHD via C-terminal phosphorylation. We observed highly specific changes in the subcellular localization of CRK2 in response to various stress treatments, and demonstrated that these localization patterns are critical for protein function and interactions. The subcellular localization and many of the cellular functions of CRK2 were dependent on phospholipase D alpha 1 (PLDɑ1) activity, and PLDɑ1 was consistently identified as one of the top proteins to interact with CRK2. Thus, we propose that CRK2 is a fundamental CRK, which acts in connection with PLDɑ1 to regulate several cellular processes during the response to environmental stimuli.