The transcription factor FveMYB117a controls leaf morphology by coordinating auxin and cytokinin signals in woodland strawberry

Abstract

Leaf morphology affects physiological activities and contributes to environment adaptation. The phytohormones auxin and cytokinin both regulate leaf shape, but how they act together to specify leaf complexity is not fully understood. In woodland strawberry (Fragaria vesca), the wild type develops trifoliate leaves, whereas myb117a mutants produce one to five leaflets with fewer serrations. Transcriptome analysis revealed that the auxin biosynthesis gene YUCCA4 (FveYUC4), the cytokinin biosynthesis gene ISOPENTENYL TRANSFERASE2 (FveIPT2), the cytokinin degradation gene CYTOKININ OXIDASE/DEHYDROGENASE1 (FveCKX1), and the transcription factor gene CUP-SHAPED COTYLEDON2 (FveCUC2a) are altered in the myb117a mutant. Accordingly, the myb117a leaves contain lower auxin levels and higher cytokinin levels compared to wild type. Moreover, treatment with the auxin transport inhibitor NPA produced simple leaves with smooth margins, whereas exogenous cytokinin application resulted in a higher percentage of four to five leaflets in myb117a. Several lines of evidence showed that FveMYB117a can directly bind to the promoters of FveYUC4 and FveCUC2a and influence their expression. Both myb117a yuc4 and myb117a cuc2a double mutants had fewer leaflets with greatly reduced or no serrations compared to myb117a, suggesting that these genes function in the same pathway. Overall, our results indicate that FveMYB117a is a transcription factor that coordinates auxin and cytokinin homeostasis in young leaves, thereby contributing to robust leaf morphogenesis in strawberry.