Over‐expression of Brassica napus phosphatidylinositol‐phospholipase C2 in canola induces significant changes in gene expression and phytohormone distribution patterns, enhances drought tolerance and promotes early flowering and maturation^†

Abstract

Phosphatidylinositol-specific phospholipase C (PtdIns-PLC2) plays a central role in the phosphatidylinositolspecific signal transduction pathway. It catalyses the hydrolysis of membrane-bound phosphatidylinositol 4,5-bisphosphate to produce two second messengers, sn-1,2-diacylglycerol and inositol 1,4,5-trisphosphate. The former is a membrane activator of protein kinase C in mammalian systems, and the latter is a Ca 2+ modulator which induces distinctive oscillating bursts of cytosolic Ca 2+ , resulting in regulation of gene expression and activation of proteins. Sustained over-expression of BnPtdIns-PLC2 in transgenic Brassica napus lines brought about an early shift from vegetative to reproductive phases, and shorter maturation periods, accompanied by notable alterations in hormonal distribution patterns in various tissues. The photosynthetic rate increased, while stomata were partly closed. Numerous gene expression changes that included induction of stressrelated genes such as glutathione S-transferase, hormoneregulated and regulatory genes, in addition to a number of kinases, calcium-regulated factors and transcription factors, were observed. Other changes included increased phytic acid levels and phytohormone organization patterns. These results suggest the importance of PtdIns-PLC2 as an elicitor of a battery of events that systematically control hormone regulation, and plant growth and development in what may be a preprogrammed mode.

Metabolomic shifts inBrassica napuslines with enhancedBnPLC2expression impact their response to low temperature stress and plant pathogens

“…23 After acclimatization, transgenic plants overexpressing BnPLC2 showed significantly elevated levels of carbohydrates associated with cellular protection, such as RFOs and smaller sugars (e.g., glucose-6-P, fructose-6-P, sucrose). Accumulation of the RFOs in transgenic lines upon acclimatization may be due to activation by the transgene of cold responsive TFs and increased availability of myo-inositol-releasing substrates such as myoinositol phosphates, in addition to the fact that overexpression of BnPLC2 has been shown to upregulate the expression of myo-inositol 1-phosphate synthase 2 for de novo synthesis of myo-inositol. The first committed step in RFO biosynthesis is the formation of galactinol from myo-inositol and UDP-galactose by the enzyme, galactinol synthase (GolS).…”

“…2 This, in addition to our findings in the current study that BnPLC2 enhancement induced, at the metabolomic level under normal growth conditions, the accumulation of higher levels of linoleate (18:2n6) and α-linolenate (18:3n3), and the fact that the latter is the precursor in the biosynthesis of JA, as well as the prominent standing of PLC/DAGK-derived PA in biotic stress tolerance, 15,16 prompted us to investigate the extent of disease resistance of transgenic plants against fungal pathogens. Sclerotinia was the pathogen of choice due to its economic importance in the canola industry.…”

“…Generally, under normal growth conditions this compound is a precursor of JA, which may explain the increase in the expression of the LOX2 enzyme in BnPLC2 overexpressing transgenic lines. 2 FFAs can also be degraded quickly by β-oxidation pathways to generate energy for the cell. Also produced through β-oxidation is acetyl-CoA which may enter the glyoxylate cycle and, through gluconeogenesis, generates additional glucose molecules.…”

“…2 Overexpression of BnPLC2 also had a significant effect on differential gene expression and hormone synthesis and distribution. 2 Some of the genes identified are known to be associated with both biotic and abiotic stress tolerance, and we showed these plants to be considerably more tolerant of drought than their corresponding NTCs.…”

“…2 Overexpression of BnPLC2 also had a significant effect on differential gene expression and hormone synthesis and distribution. 2 Some of the genes identified are known to be associated with both biotic and abiotic stress tolerance, and we showed these plants to be considerably more tolerant of drought than their corresponding NTCs. Of particular interest to the current study are genes such as lipoxygenase 2 (LOX2), a principal enzyme in jasmonic acid (JA) biosynthesis, and several JA-responsive genes and proteins, including strictosidine synthase and other disease-associated defense genes (e.g., glucanases and chitinases), whose change in expression implies an effect of BnPLC2 enhancement toward priming stress tolerance, 2 presumably synergistically with innate defense mechanisms.…”