A drought stress-induced MYB transcription factor regulates pavement cell shape in leaves of European aspen (Populus tremula).

Leaf pavement cells of many plant species develop jigsaw puzzle-like shapes in which neighboring cells interdigitate, providing an ideal model for the study of cell shape regulation. Such shapes are likely to reduce tissue-wide mechanical stress, which is influenced by environmental conditions, such as drought stress. We analyzed pavement cell shape complexity in a natural population of European aspen (Populus tremula) genotypes and used a genome-wide association study (GWAS) to identify a candidate gene in cell shape regulation, Potra2n8c18226, encoding the transcription factor MYB305a. We subsequently validated a role for MYB305a in regulating aspen leaf pavement cell shape. We then demonstrated that drought stress strongly induces MYB305a promoter expression in these cells and provided evidence that MYB305a plays a role in regulating pavement cell shape in response to drought. Finally, we observed correlations of pavement cell shape complexity with water-use efficiency and average precipitation at the original sampling sites, in the natural aspen population. Taken together, our results suggest climatic variables affect shape complexity of pavement cells in aspen leaf and provide a foundation for future mechanistic studies on this process, by implicating the involvement of the transcription factor MY305a.