PLOS Genet：生长素原位合成和叶边缘发育调控新机制

　　

    8月16日，国际期刊《PLOS Genetics》杂志在线发表中科院薛红卫研究组题为“Arabidopsis type II phosphatidylinositol 4-kinase PI4Kγ5 regulates auxin biosynthesis and leaf margin serration through interacting with and affecting the cleavage of a membrane-bound NAC transcription factor”的研究论文，该研究发现拟南芥磷脂酰肌醇-4-激酶PI4Kγ5通过调控膜定位转录因子ANAC078的剪切，进而影响生长素的原位合成和叶边缘发育。

      高等植物叶边缘发育是叶形态建成的最后步骤，其正常发育对于叶形态建成和叶片形状形成非常重要。目前的研究表明叶边缘发育的调控主要涉及叶片细胞的分裂，此外，生长素在叶边缘发育过程中也发挥了重要调控作用。薛红卫研究组前期在磷脂酰肌醇信号作用及该途径与生长素互作调控植物生长发育方面开展了系统工作，进一步的遗传学研究发现II类磷脂酰肌醇-4-激酶PI4Kγ5的功能缺失体pi4kγ5-1呈现叶裂增强的表型，细胞学观察和分析发现突变体叶裂增强是由于生长素促进的叶边缘突起处细胞分裂增加导致的，pi4kγ5-1的叶边缘生长素含量增加。进一步的研究表明，PI4Kγ5与膜定位转录因子ANAC078相互作用并促进其蛋白剪切及入核，剪切入核的ANAC078直接抑制生长素合成相关基因YUC2和YUC4的转录及生长素的合成，维持正常细胞分裂和叶边缘发育。

      转录因子通过调控下游基因转录发挥重要调控作用，近来的研究表明一些膜（质膜、细胞器膜等）定位的转录因子通过蛋白剪切后入核调控基因转录，本研究不但阐明了磷脂酰肌醇信号调控生长素原位合成及细胞分裂的机制，也为膜定位转录因子剪切入核的调控机制提供了重要线索。

      本研究得到了国家自然科学基金委的资助。由唐勇、赵春艳等完成。

pi4kγ5-1突变体表型(左)及PI4Kγ5-ANAC078调控生长素合成模式图(右)。

原文摘要：

Arabidopsis Type II Phosphatidylinositol 4-Kinase PI4Kγ5 Regulates Auxin Biosynthesis and Leaf Margin Development through Interacting with Membrane-Bound Transcription Factor ANAC078

Normal leaf margin development is important for leaf morphogenesis and contributes to diverse leaf shapes in higher plants. We here 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 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. Studies revealed 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. Western blot analysis indeed showed that ANAC078 deleting of carboxyl terminal is significantly reduced in pi4kγ5–1, indicating that PI4Kγ5 is important for the cleavage of ANAC078. This is consistent with the subcellular localization observation showing that fluorescence by GFP-ANAC078 is detected at plasma membrane but not nucleus in pi4kγ5–1 mutant and that expression of ANAC078 deleting of carboxyl terminal, driven by PI4Kγ5 promoter, could rescue the leaf serration defects of pi4kγ5–1. Further analysis showed that ANAC078 suppresses the auxin synthesis by directly binding and regulating the expression of auxin synthesis-related genes. These results indicate that PI4Kγ5 interacts with ANAC078 to negatively regulate auxin synthesis and hence influences cell proliferation and leaf development, providing informative clues for the regulation of in situ auxin synthesis and cell division, as well as the cleavage and functional mechanism of membrane-bound transcription factors.