Arabidopsis Leaf Flatness Is Regulated by PPD2 and NINJA through Repression of <i>CYCLIN D3</i> Genes

Abstract

In Arabidopsis (<i>Arabidopsis thaliana</i>), reduced expression of the transcriptional regulator <i>PEAPOD2</i> (<i>PPD2</i>) results in propeller-like rosettes with enlarged and dome-shaped leaves. However, the molecular and cellular processes underlying this peculiar phenotype remain elusive. Here, we studied the interaction between PPD2 and NOVEL INTERACTOR OF JAZ (NINJA) and demonstrated that <i>ninja</i> loss-of-function plants produce rosettes with dome-shaped leaves similar to those of <i>ppd</i> mutants but without the increase in size. We showed that <i>ninja</i> mutants have a convex-shaped primary cell cycle arrest front, putatively leading to excessive cell division in the central leaf blade region. Furthermore, <i>ppd</i> and <i>ninja</i> mutants have a similar increase in the expression of <i>CYCLIN D3;2</i> (<i>CYCD3;2</i>), and ectopic overexpression of <i>CYCD3;2</i> phenocopies the <i>ppd</i> and <i>ninja</i> rosette and leaf shape phenotypes without affecting the size. Our results reveal a pivotal contribution of NINJA in leaf development, in addition to its well-studied function in jasmonate signaling, and imply a new function for D3-type cyclins in, at least partially, uncoupling the size and shape phenotypes of <i>ppd</i> leaves.