The Effect and Regulation Mechanism of Powdery Mildew on Wheat Grain Carbon Metabolism

The effects of powdery mildew on gene expressions and activities of carbon (C) metabolism enzymes in Zhengmai 103 (resistant) and Xi'nong 979 (susceptible) are studied. Under severe powdery mildew, expressions and activities of sucrose synthase, uridine-diphosphate glucose pyrophosphorylase, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and cytosolic alpha-1,4-glucan phosphorylase decrease at 20 or 25-30 days after anthesis, and total soluble sugars content also decreases. It indicates that the first part of C metabolism (sucrose degradation) changes and total C flux reduces. Meanwhile, decreases in expressions and activities of adenosine-diphosphate glucose pyrophosphorylase (AGPase), soluble starch synthase (SSS), starch-branching enzyme I and II (SBEI and SBEII), and plastidic alpha-1,4-glucan phosphorylase coincide with decreases in amylopectin content, whereas increases in granule-bound starch synthase I (GBSSI) expression and activity coincide with increases in amylose content. It shows that the second part of C metabolism (starch synthesis) changes. Therefore, powdery mildew alters C metabolism. In addition, it also induces defense responses in grains, such as the up-regulation of a defense-related protein endogenous alpha-amylase/subtilisin inhibitor. Since GAPDH, AGPase, SSS, SBEII, and GBSSI are regulated by redox, changes of C metabolism are mainly regulated by cellular redox status.