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The remarkable diversity of leaf forms allows plants to adapt to their living environment. In general, leaf diversity is shaped by leaf complexity (compound or simple) and leaf margin pattern (entire, serrated, or lobed). Prior studies in multiple species have uncovered a conserved module of CUC2-auxin that regulates both leaf complexity and margin serration. How this module is regulated in different species to contribute to the species-specific leaf form is unclear. Furthermore, the mechanistic connection between leaf complexity and leaf serration regulation is not well studied. Strawberry has trifoliate compound leaves with serrations at the margin. In the wild strawberry Fragaria vesca, a mutant named salad was isolated that showed deeper leaf serrations but normal leaf complexity. SALAD encodes a single-Myb domain protein and is expressed at the leaf margin. Genetic analysis showed that cuc2a is epistatic to salad, indicating that SALAD normally limits leaf serration depth by repressing CUC2a expression. When both Arabidopsis homologs of SALAD were knocked out, deeper serrations were observed in Arabidopsis rosette leaves, supporting a conserved function of SALAD in leaf serration regulation. We incorporated the analysis of a third strawberry mutant simple leaf 1 (sl1) with reduced leaf complexity but normal leaf serration. We showed that SL1 and SALAD independently regulate CUC2a at different stages of leaf development to, respectively, regulate leaf complexity and leaf serration. Our results provide a clear and simple mechanism of how leaf complexity and leaf serration are coordinately as well as independently regulated to achieve diverse leaf forms. 

Abstract The R2R3-MYB transcription factor FveMYB10 is a major regulator of anthocyanin pigmentation in the red strawberry fruits. fvemyb10 loss-of-function mutants form yellow fruits but still accumulate purple-colored anthocyanins in the petioles, suggesting that anthocyanin biosynthesis is under distinct regulation in fruits and petioles. We identified a green petioles (gp)-1 mutant from chemical mutagenesis in the diploid wild strawberry Fragaria vesca that lacks anthocyanins in petioles. Using mapping-by-sequencing and transient functional assays, we confirmed that the causative mutation resides in a FveMYB10-Like (MYB10L) gene and that FveMYB10 and FveMYB10L function independently in the fruit and petiole respectively. In addition to their tissue-specific regulation, FveMYB10 and FveMYB10L respond differently to changes in light quality, produce distinct anthocyanin compositions, and preferentially activate different downstream anthocyanin biosynthesis genes in their respective tissues. This work identifies a new regulator of anthocyanin synthesis and demonstrates that two paralogous MYB genes with specialized functions enable tissue-specific regulation of anthocyanin biosynthesis in fruit and petiole tissues.