Browsing by Subject "Gerbera"

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  • Zhao, Yafei; Zhang, Teng; Broholm, Suvi K.; Tähtiharju, Sari; Mouhu, Katriina; Albert, Victor A; Teeri, Teemu H.; Elomaa, Paula (2016)
    The evolutionary success of Asteraceae, the largest family of flowering plants, has been attributed to the unique inflorescence architecture of the family, which superficially resembles an individual flower. Here, we show that Asteraceae inflorescences (flower heads, or capitula) resemble solitary flowers not only morphologically but also at the molecular level. By conducting functional analyses for orthologs of the flower meristem identity genes LEAFY (LFY) and UNUSUAL FLORAL ORGANS (UFO) in Gerbera hybrida, we show that GhUFO is the master regulator of flower meristem identity, while GhLFY has evolved a novel, homeotic function during the evolution of head-like inflorescences. Resembling LFY expression in a single flower meristem, uniform expression of GhLFY in the inflorescence meristem defines the capitulum as a determinate structure that can assume floral fate upon ectopic GhUFO expression. We also show that GhLFY uniquely regulates the ontogeny of outer, expanded ray flowers but not inner, compact disc flowers, indicating that the distinction of different flower types in Asteraceae is connected with their independent evolutionary origins from separate branching systems.
  • Shiradhonkar, Rohan (Helsingin yliopisto, 2019)
    The complex inflorescence architecture in Asteraceae is characterized by the presence of morphologically distinct flowers having specialized functions. In gerbera, the presence of three different flower types (ray, trans and disc), intricate inflorescence organization and an underlying complex molecular control makes it an excellent target for research on functional genomics, flower development and evolution. The genes governing flower development have been shown to have undergone sub- and neo-functionalization in gerbera leading to morphological features that are not present in the conventional model plant species. The genes encoding the CYC2 subclade of CYC/TB1-like TCP domain transcription factors are known to regulate the flower type identity in gerbera inflorescence. Although most genes of the CYC2 subclade have demonstrated functional redundancy, one such gene, GhCYC5, was found to have diverged function in regulating rate of initiation of flowers. This study aimed at investigating and affirming the function of GhCYC5 by studying two RNAi lines. Phenotypic analysis of the RNAi inflorescences showed that the length of ray ligules was significantly decreased along with the number of disc flowers and the number of involucral bracts. However, gene expression analysis could not confirm the downregulation of GhCYC5 in the RNAi lines mainly due to low endogenous expression of the gene. However, GhCYC3, another CYC2 clade gene was found to be downregulated due to the off-target silencing effect of the RNAi product and the observed phenotype was associated with suppression of GhCYC3. Further, the role of GhCYC5 in regulating the rate of involucral bract and flower initiation was unclear based on the SEM imaging and expression analysis of the inflorescence meristem, and still requires further studies.
  • Cai, Xiaobo (Helsingin yliopisto, 2020)
    Inflorescence meristems (IMs) either keep producing new flowers, thereby being indeterminate, or terminate after initiation of a finite number of flowers, thereby being determinate. Gerbera hybrida (Asteraceae) has determinate inflorescences. It has been found that the LEAFY (LFY) homolog GhLFY and SEPALLATA (SEP)-like GRCD2/7 promote IM termination in Gerbera as LFY and SEP genes do in Arabidopsis. Downregulation of their expression in Gerbera leads to indeterminate inflorescences. Considering the roles of WUSCHEL (WUS), CLAVATA3 (CLV3) and SHOOT MERISTEMLESS (STM) in meristem maintenance and of TERMINAL FLOWER 1 (TFL1) in IM determinacy in Arabidopsis, it is possible that GhLFY and GRCD2/7 contribute to IM termination by regulating the expression of the homologs of these genes, namely GhWUSb, GhWOX2a, GhCLV3, GhSTM and GhTFL1. It is also possible that GhLFY upregulates the expression of GRCD2/7 in Gerbera, since LFY upregulates SEP gene expression in Arabidopsis. To test these hypotheses, the expression of these candidate genes in Gerbera IMs was compared between IM-expanding and terminating stages, as well as between transgenic plants with downregulated GhLFY or GRCD2/7 expression and wild-type plants. In addition, the pOpOn2 inducible expression vector was used in Gerbera for the first time, in order to induce GhWUSb overexpression in transgenic plants and to study the function of GhWUSb in IM determinacy. Expression analysis showed that during IM termination, GRCD7 expression was upregulated, while the expression of GhWUSb, GhCLV3 and GhWOX2a was downregulated. GhLFY upregulated the expression of GRCD7, and both of them downregulated the expression of GhWUSb, GhCLV3 and GhWOX2a. The expression of GhSTM and GRCD2 was neither affected by IM termination nor regulated by GhLFY or GRCD7. GhTFL1 expression was not detected in any IM samples. Induced GhWUSb overexpression delayed IM termination, confirming the role of GhWUSb in meristem maintenance. These results suggest that GRCD7 may contribute to IM termination by suppressing the expression of the meristem maintenance gene GhWUSb, and the upregulation of GRCD7 by GhLFY may be required for IM termination. GRCD2 and GhSTM may not play a significant role in inflorescence determinacy.
  • Sultana, Dalia Mrs (Helsingin yliopisto, 2021)
    Anthocyanins are an important class of flavonoids under the class of phenolic compounds and contribute to flower color variation. Gerbera hybrida is a flowering plant of Asteraceae family having mainly two colors of flowers – orange and red. Dihydroflavonol 4-reductase (DFR) is a key enzyme catalyzing a reaction in anthocyanin biosynthesis, the reduction of dihydroflavonols to leucoanthocyanidins. GDFR1-2 and GDFR1-3 are two allelic forms of gerbera DFR differing in substrate specificity for the dihydroflavonols - dihydrokaempferol, dihydroquercetin and dihydromyricetin and also differ in 13 amino acids where eight are considered to be important for substrate specificity. GDFR1-2 has strong preference for dihydrokaempferol and GDFR1-3 doesn’t have any preference for the three substrates. In order to find out the amino acids responsible for substrate specificity, swap mutations were generated between GDFR1-2 and GDFR1-3 by two PCR methods– first, running separate PCR from the templates of GDFR1-2 and GDFR1-3, making a heteroduplex by mixing separate PCR where non-matching nucleotides are expected to be corrected by E. coli and, second, by running PCR from mixed templates with short extension time of PCR to make swaps by template switching. The second method was found more effective than the first method. 81 lines (named GDAT1-81) were sequenced and 35 unique swap mutants were found. In this work the DFR assay was done from six randomly picked GDAT lines where GDAT5 had a swap in one amino acid showing still a similar pattern of substrate specificity as the reference (GDFR1-3) indicating that the mutated amino acid doesn’t have any role in substrate specificity. GDAT14 had an extra mutation (S167P) along with 2 swaps showing incapability of reducing dihydrokaempferol, demonstrating that the mutated amino acids are important and other 4 lines were identical to either GDFR1-2 or to GDFR1-3. This was a preliminary test with 6 lines. In order to get more explanations about the roles of amino acids in substrate specificity, DFR assay was done for all the 81 lines in experiments outside of this thesis and five patterns of substrate specificity were identified indicating that substrate specificity of DFR can be altered by changing only three important amino acids. The amino acids at the position 85,135 and 181 in DFR coding sequence have been identified having important roles in substrate specificity. In addition, the amino acid at position 167 may have a function in making the gerbera DFR able to reduce dihydrokaempferol.
  • Deng, Xianbao; Elomaa, Paula; Nguyen, Cuong X.; Hytonen, Timo; Valkonen, Jari P. T.; Teeri, Teemu H. (2012)