Functional Analysis Of PPLAⅢδ Gene In Arabidopsis And Brassica Napus

The members of the patatin-related phospholipase subfamily Ⅲ (pPLAⅢs) have been implicated in the auxin response. However, it is not clear whether and how these genes affect plant and cell morphogenesis. Here, we studied the roles of the patatin-related phospholipase pPLAⅢδ in auxin-responsive cell morphology and organ size in Arabidopsis and Brassica napus.We utilized the pPLAⅢδT-DNA mutant (pPLAⅢδ-KO), the overexpression lines in Arabidopsis (pPLAⅢδ-OE) and Brassica to study the influence of the altered pPLAⅢδexpression in the plant morphology, cytology, metabolic products as well as the expressions of other genes.1 GUS staining and gene expression analyses showed that pPLAⅢδ expressed in multiple organs, while it preferred the roots and the immatural tissues.2 The subcellular localization analysis showed pPLAⅢδ was localized at the plasma membrane.3 pPLAⅢδ-OE displayed the lowered plant height, the shortened and widened internodes,the smaller, thicker leaves and so on, suggesting pPLAⅢδinhibited longitudinal growth but promoted transverse growth in most organs of Arabidopsis and Brassica napus.4 Compared to wild-type plants, pPLAⅢδ-KO plants exhibited enhanced cell elongation in hypocotyls, and pPLAⅢδ-OE plants displayed broadened radial cell growth of hypocotyl and reduced leaf pavement cell polarity, suggesting pPLAⅢδ was propably involved in the cell morphogenesis.5 The hypocotyl phenotype in pPLAⅢδ mutants resembles the "triple response" to ethylene. According to the gene expression analysis, ACS4 and ACS5involved in the ethylene biosynthesis were up-regulated by 2.5-fold on average in two OE lines compared with WT plants, indicating changing pPLAⅢδ expression impaced the biosynthesis of ethylene.6 The endogenous auxin distribution was disturbed in plants with alteredpPLAⅢδexpression. Through detecting the auxin content in pPLAⅢδ mutants and DR::GUS staining,wefound altering pPLAⅢδ expression influenced the endogenous auxin distribution.7pPLAⅢδ-OE and KO plants exhibited different sensitivities to indole-3-acetic acid-promoted hypocotyl elongation at both light and dark conditions. Gene expression analysis of auxin-induced genes in the dark showed that OE plants maintained a higher auxin response compared with WT and KO plants after treatment with 1μM IAA for 12 h. Following treatment with 10 μM IAA for 30 min in the light, early auxin-induced genes were significantly up-regulated in two OE plant lines. Such results showed the different auxin responses in KO and OE.8Microarray profiling revealed that large number of genes involved in auxin response and cell morphogenesis were upregulated in OE stems.9We cloned 8 and 11 sequences from DNA and cDNA of Brassica plant, respectively, and their similarity to the amino acid sequence of pPLAⅢδ was up to 88%.These data suggest that the PLAⅢδgene plays an important role in plant cell morphology and organ size through its involvement in the regulation of auxin distribution inArabidopsis and Brassica napus. This study enrichs our understanding of the biological functions of pPLAⅢδ and further confirmd the important role of phospholipid-depended signal transduction in the plant auxin regulation and cell polaried growth.