Phospholipases Dα and δ are involved in local and systemic wound responses of cotton (G. hirsutum)

Characterization and evolutionary diversification of the phospholipase D gene family in mosses

Plant phospholipase D (PLD) exerts important roles in various biological processes, such as intracellular signaling and morphological development. Our knowledge about early land plant PLDs is still underdeveloped. In this study, we identified 84 PLD genes in six mosses, i.e., Physcomitrella patens, Ceratodon purpureus, Fontinalis antipyretica, Pleurozium schreberi, Sphagnum magellanicum, and Sphagnum fallax. These PLDs were classified into four clades (I-IV). We showed that PLD underwent rapid expansion in mosses. A total of six conserved domains and two core HKD motifs were detected. Structure analysis uncovered that the moss PLDs from within a clade generally exhibited similar exon-intron organization. Cis-elements prediction and expression analyses indicated that P. patens PLDs had key roles in stress responsiveness and plant development. Particularly, about half of the P. patens PLDs (e.g., PpPLD1, PpPLD2, and PpPLD5) were differentially expressed under biotic and abiotic stresses. We also determined the expression pattern of P. patens PLD genes in various tissues and at different stages of development. Although the moss, clubmoss, liverwort, and fern PLDs evolved largely under functional constraints, we found episodic positive selection in the moss PLDs, e.g., C. purpureus PLD2 and P. patens PLD11. We infer that the evolutionary force acting on the PLDs may have facilitated moss colonization of land. Our work provides valuable insights into the diversification of moss PLD genes, and can be used for future studies of their functions.

Effects of extracellular ATP on local and systemic responses of bean (Phaseolus vulgaris L) leaves to wounding

Wounding increased the extracellular Adenosine 5'-triphosphate (eATP) level of kidney bean leaves. Treatment with wounding or exogenous ATP increased the hydrogen peroxide (H₂O₂) content, activities of catalase and polyphenol oxidase, and malondialdehyde content in both the treated and systemic leaves. Pre-treatment with ATP-degrading enzyme, apyrase, to the wounded leaves reduced the wound-induced local and systemic increases in H₂O₂ content, activities of catalase and polyphenol oxidase, and malondialdehyde content. Application of dimethylthiourea (DMTU) and diphenylene iodonium (DPI) to the wounded and ATP-treated leaves, respectively, reduced the wound- and ATP-induced local and systemic increases in H₂O₂ content, activities of catalase and polyphenol oxidase, and malondialdehyde content. Moreover, the wound- and ATP-induced systemic increases of these physiological parameters were suppressed when DMTU or DPI applied to leaf petiole of the wounded and ATP-treated leaves. These results suggest that eATP at wounded sites could mediate the wound-induced local and systemic responses by H₂O₂-dependent signal transduction.

Study of the Involvement of Phosphatidic Acid Formation in the Expression of Wound-Responsive Genes in Cotton

Plants use phospholipase D (PLD, EC 3.1.4.4)/phosphatidic acid (PtdOH) for the transduction of environmental signals including those coming from wounding. Based on our previous findings suggesting that wound-induced PLDα-derived PtdOH can act as a local signaling molecule in cotton (Gossypium hirsutum), we show that wounding immediately increases local NADPH oxidase (NADPHox) and cellulose synthase A (CeSA) gene expression. After developing a novel fluorimetric assay for the investigation of n-butanol inhibitory effect on PLD activity, we show that only NADPHox gene upregulation is reduced when n-butanol is applied prior to wounding. This suggests that NADPHox is a possible downstream target of PLD function, while a different CeSA-involving response system may exist in cotton. Overall, this study provides new knowledge on signal-transduction mechanisms following wounding of cotton leaves.