Gharf16-1 Modulates Leaf Development By Transcriptionally Regulating Theghknox2-1gene In Cotton

The leaf is a crucial organ evolved with remarkable morphological diversity to maximize plant photosynthesis. The leaf shape is a key trait that affects photosynthesis, flowering rates, disease resistance and yield. Although many genes regulating leaf development have been identified in the past years, the precise regulatory architecture underlying the generation of diverse leaf shapes remains to be elucidated. We used cotton as a reference model to probe the genetic framework underlying divergent leaf forms. Comparative transcriptome analysis revealed that theGhARF16-1andGhKNOX2-1genes might be potential regulators of leaf shape. We functionally characterized the auxin-responsive factor ARF16-1 acting upstream ofGhKNOX2-1to determine leaf morphology in cotton. The transcription ofGhARF16-1was significantly higher in lobed-leaved cotton than in smooth-leaved cotton. Furthermore, the overexpression ofGhARF16-1led to the up-regulation ofGhKNOX2-1and resulted in more and deeper serrations in cotton leaves, similar to the leaf shape of cotton plants overexpressingGhKNOX2-1. We found that GhARF16-1 specifically bound to the promoter ofGhKNOX2-1to induce its expression. The heterologous expression ofGhARF16-1andGhKNOX2-1inArabidopsisled to lobed and curly leaves, and a genetic analysis revealed thatGhKNOX2-1is epistatic toGhARF16-1inArabidopsis, suggesting that the GhARF16-1 andGhKNOX2-1interaction paradigm also functions to regulate leaf shape inArabidopsis. To our knowledge, our results uncover a novel mechanism by which auxin, through the key component ARF16-1 and its downstream-activated geneKNOX2-1, determines leaf morphology in eudicots.