Patatin-Related Phospholipase AtpPLAIIIα Affects Lignification of Xylem in Arabidopsis and Hybrid Poplars

Lipid acyl hydrolase are a diverse group of enzymes that hydrolyze the ester or amide bonds of fatty acid in plant lipids. Patatin-related phospholipase AIIIs (pPLAIIIs) are one of major lipid acyl hydrolases that are less closely related to potato tuber patatins and are plant-specific. Recently, overexpression of ginseng-derived PgpPLAIIIβ was reported to be involved in the reduced level of lignin content in Arabidopsis and the mature xylem layer of poplar. The presence of lignin-polysaccharides renders cell walls recalcitrant for pulping and biofuel production. The tissue-specific regulation of lignin biosynthesis, without altering all xylem in plants, can be utilized usefully by keeping mechanical strength and resistance to various environmental stimuli. To identify another pPLAIII homolog from Arabidopsis, constitutively overexpressed AtpPLAIIIα was characterized for xylem lignification in two well-studied model plants, Arabidopsis and poplar. The characterization of gene function in annual and perennial plants with respect to lignin biosynthesis revealed the functional redundancy of less lignification via downregulation of lignin biosynthesis-related genes.

The Arabidopsis Patatin-Like Protein 2 (PLP2) Plays an Essential Role in Cell Death Execution and Differentially Affects Biosynthesis of Oxylipins and Resistance to Pathogens

We previously reported that patatin-like protein 2 (PLP2), a pathogen-induced patatin-like lipid acyl hydrolase, promotes cell death and negatively affects Arabidopsis resistance to the fungus Botrytis cinerea and to the bacteria Pseudomonas syringae. We show here that, on the contrary, PLP2 contributes to resistance to Cucumber mosaic virus, an obligate parasite inducing the hypersensitive response. These contrasted impacts on different pathosystems were also reflected by differential effects on defense gene induction. To examine a possible link between PLP2 lipolytic activity and oxylipin metabolism, gene expression profiling was performed and identified B. cinerea among these pathogens as the strongest inducer of most oxylipin biosynthetic genes. Quantitative oxylipin profiling in wild-type and PLP2-modified, Botrytis-challenged plants established the massive accumulation of oxidized fatty acid derivatives in infected leaves. Several compounds previously described as modulating plant tissue damage and issued from the α-dioxygenase pathway were found to accumulate in a PLP2-dependent manner. Finally, the contribution of PLP2 to genetically controlled cell death was evaluated using PLP2-silenced or -overexpressing plants crossed with the lesion mimic mutant vascular-associated death 1 (vad1). Phenotypic analysis of double-mutant progeny showed that PLP2 expression strongly promotes necrotic symptoms in vad1 leaves. Collectively, our data indicate that PLP2 is an integral component of the plant cell death execution machinery, possibly providing fatty acid precursors for the biosynthesis of specific oxylipins and differentially affecting resistance to pathogens with distinct lifestyles.