Translocation of phospholipase A2α to apoplasts is modulated by developmental stages and bacterial infection in Arabidopsis

Phospholipase A2 (PLA2) hydrolyzes phospholipids at the sn-2 position to yield lysophospholipids and free fatty acids. Of the four paralogs expressed in Arabidopsis, the cellular functions of PLA2α in planta are poorly understood. The present study shows that PLA2α possesses unique characteristics in terms of spatiotemporal subcellular localization, as compared with the other paralogs that remain in the ER and/or Golgi apparatus during secretory processes. Only PLA2α is secreted out to extracellular spaces, and its secretion to apoplasts is modulated according to the developmental stages of plant tissues. Observation of PLA2α-RFP transgenic plants suggests that PLA2α localizes mostly at the Golgi bodies in actively growing leaf tissues, but is gradually translocated to apoplasts as the leaves become mature. When Pseudomonas syringae pv.~tomato DC3000 carrying the avirulent factor avrRpm1 infects the apoplasts of host plants, PLA2α rapidly translocates to the apoplasts where bacteria attempt to become established. PLA2α promoter::GUS assays show that PLA2α gene expression is controlled in a developmental stage- and tissue-specific manner. It would be interesting to investigate if PLA2α functions in plant defense responses at apoplasts where secreted PLA2α confronts with invading pathogens

Threonine 286 of fatty acid desaturase 7 is essential for ω-3 fatty acid desaturation in the green microalga Chlamydomonas reinhardtii

Omega-3 fatty acid desaturases catalyze the conversion of dienoic fatty acids (C18:2 and C16:2) into trienoic fatty acids (C18:3 and C16:3), accounting for more than 50% of the total fatty acids in higher plants and the green microalga Chlamydomonas reinhardtii. Here, we describe a Thr residue located in the fourth transmembrane domain of fatty acid desaturase 7 (FAD7) that is essential for the biosynthesis of ω-3 fatty acids in C. reinhardtii. The ω-3 fatty acid deficiency in strain CC-620, which contains a putative missense mutation at Thr286 of CrFAD7, was recovered by the overexpression of CC-125 CrFAD7. A Ser substitution in position 286 was able to partially complement the phenotype of the ω-3 fatty acid deficiency, but other substitution variants, such as Tyr, His, Cys, and Gly, failed to do so. Prediction of the phosphorylation target site revealed that Thr286 may be phosphorylated. Analysis of the structural conformation of CC-620 CrFAD7 via topology prediction (and bends in the helix) shows that this missense mutation may collapse the catalytic structure of CrFAD7. Taken together, this study suggests that Thr286 is essential for the maintaining the catalytic structure of CrFAD7