The dual role of a bHLH protein: Is SCRM1 / ICE1 an integrator of cold-stress and stomatal fate signaling?
Final Report Abstract
In the scope of the DFG research fellowship, the specific role of the bHLH transcription factor SCRM in different stages of stomatal development was analyzed. A compendium of meristemoid-expressed genes was generated using a transcriptome approach. Comparison of this dataset with publicly available data of other plant stem-cell populations (SAM and RAM) revealed little overlap between these three populations, but underlined the general importance of cellcell signaling in stem-cell maintenance and differentiation, and a potential role of SCHIZORIZA in stomatal development. Mining of the meristemoid dataset revealed a subset of genes involved in plant hormone metabolism and signaling, specifically cytokinin and jasmonate signaling. Furthermore, a novel polarity factor, POLAR, was found, that is specifically expressed in asymmetrically dividing meristemoids and localizes distally 2 h prior to the formation of the division plane. This localization pattern is partially dependent on BASL, although no direct interaction between BASL and POLAR could be established. The promoter of POLAR contains three E-box motifs, making it a likely target of either SCRM, SPCH, or both bHLH transcription factors. SCRM has previously been shown to bind to E-boxes in vitro, and I observed binding of SCRM to promoter regions that contain E-boxes, i.e. the EPF2, TMM and SCRM promoters, suggesting that SCRM directly targets these genes and is also capable of auto activation. Interestingly, no binding of SPCH to either the EPF2 or TMM promoter was observed, suggesting that SCRM dimerizes with another, potentially novel factor to bind to these promoters. This factor remains to be identified. To elucidate genome-wide binding patterns of SCRM at different stages of stomatal development, the INTACT system was modified to allow for the isolation of stem-cell like meristemoids, differentiating meristemoids / young guard mother cells and immature guard cells. These newly developed plant lines will be used to perform ChIPseq using SCRM for IP. Preliminary analysis of the chromatin landscape of these cell stages, that was obtained by digital DNaseI mapping revealed striking differences in the chromatin structure between these cell stages. These analyses will allow for the identification of regulatory elements within these cell types and shed light on the diverse role of SCRM in stomatal development.
Publications
- (2011). Molecular profiling of stomatal meristemoids reveals new component of asymmetric cell division and commonalities among stem-cell populations in Arabidopsis. Plant Cell, 23, 3260-3275
LJ Pillitteri, KM Peterson, RJ Horst, KU Torii
- (2012). Regulation of inflorescence architecture by inter-tissue-layer ligandreceptor communication between endodermis and phloem. Proceedings of the National Academy of Sciences, 109(16), 6337-6342
N Uchida, JS Lee, RJ Horst, HH Lai, R Kajita, T Kakimoto, M Tatsuo and KU Torii
