The margin development is the final step of plant leaf morphogenesis, which is important for leaf morphogenesis and contributes largely to diverse leaf shapes of higher plants. A research group led by Prof. XUE Hongwei at Shanghai Institute of Plant Physiology and Ecology (SIPPE), Shanghai Institutes for Biological Sciences (SIBS), CAS show the crucial roles of an atypical type II phosphatidylinositol 4-kinase, PI4Kγ5, in Arabidopsis leaf margin development.

PI4Kγ5 presents a dynamics expression pattern along with leaf development and a transfer-DNA (T-DNA) mutant lacking PI4Kγ5, pi4kγ5–1, presents serrated leaves, which is resulted from the accelerated cell division and increased auxin concentration at serration tips. Biochemical analyses reveal that PI4Kγ5 interacts with and phosphorylates a membrane-bound NAC transcription factor, ANAC078. Previous studies demonstrated that membrane-bound transcription factors regulate gene transcription by undergoing proteolytic process to translocate into nucleus, and ANAC078 undergoes proteolysis by cleaving off the transmembrane region and carboxyl terminal. Further genetic analysis confirm that PI4Kγ5 is crucial for the cleavage and normal function of ANAC078, which is consistent with that expression of ANAC078 deleting of carboxyl terminal, driven by PI4Kγ5 promoter, could rescue the leaf serration defects of pi4kγ5–1. Further analyses show that ANAC078 suppresses the auxin synthesis by directly binding and regulating the expression of auxin synthesis-related genes.

These results together indicate that PI4Kγ5-ANAC078 module downregulates auxin level during leaf development (serration) and provide novel insights into the regulation of local auxin biosynthesis and cell division, as well as the cleavage and functional mechanism of membrane-bound transcription factors.

The article entitled “Arabidopsis Type II Phosphatidylinositol 4-Kinase PI4Kγ5 Regulates Auxin Biosynthesis and Leaf Margin Development through Interacting with Membrane-Bound Transcription Factor ANAC078” was published online on August 16, 2016 in PLOS Genetics.

This study was supported by the National Natural Science Foundation of China (NSFC).

AUTHOR CONTACT:
Prof. Hongwei Xue
E-mail: hwxue@sibs.ac.cn
Shanghai Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 
Shanghai, China

Identification and phenotypic analysis of knockout mutant pi4ky5-1

A hypothetic model how PI4Kγ5 ANAC078 module regulates auxin synthesis and leaf development.