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Jasmonic acid (JA) plays pivotal roles in diverse plant biological processes, including wound response. Chloroplast lipid hydrolysis is a critical step for JA biosynthesis, but the mechanism of this process remains elusive. We report here that DONGLE (DGL), a homolog of DEFECTIVE IN ANTHER DEHISCENCE1 (DAD1), encodes a chloroplast-targeted lipase with strong galactolipase and weak phospholipase A(1) activity. DGL is expressed in the leaves and has a specific role in maintaining basal JA content under normal conditions, and this expression regulates vegetative growth and is required for a rapid JA burst after wounding. During wounding, DGL and DAD1 have partially redundant functions for JA production, but they show different induction kinetics, indicating temporally separated roles: DGL plays a role in the early phase of JA production, and DAD1 plays a role in the late phase of JA production. Whereas DGL and DAD1 are necessary and sufficient for JA production, phospholipase D appears to modulate wound response by stimulating DGL and DAD1 expression.

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To elucidate the cellular functions of phospholipase A 2 in plants, an Arabidopsis cDNA encoding a secretory low molecular weight phospholipase A 2 ( At sPLA 2 ␤ ) was isolated. Phenotype analyses of transgenic plants showed that overexpression of At sPLA 2 ␤ promotes cell elongation, resulting in prolonged leaf petioles and inflorescence stems, whereas RNA interferencemediated silencing of At sPLA 2 ␤ expression retards cell elongation, resulting in shortened leaf petioles and stems. At sPLA 2 ␤ is expressed in the cortical, vascular, and endodermal cells of the actively growing tissues of inflorescence stems and hypocotyls. At sPLA 2 ␤ then is secreted into the extracellular spaces, where signaling for cell wall acidification is thought to occur. At sPLA 2 ␤ -overexpressing or -silenced transgenic plants showed altered gravitropism in inflorescence stems and hypocotyls. At sPLA 2 ␤ expression is induced rapidly by auxin treatment and in the curving regions of inflorescence stems undergoing the gravitropic response. These results suggest that At sPLA 2 ␤ regulates the process of cell elongation and plays important roles in shoot gravitropism by mediating auxin-induced cell elongation.

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