Characterization of Starch Physicochemical Properties and Grain Transcriptome Reveal the Mechanism for Resistant Starch Accumulation

Abstract

Understanding the physicochemical properties of starch during grain development and the mechanism for resistant starch (RS) accumulation will provide useful information for improving the RS content of wheat. The grains from wheat mutant lines with high RS contents and their corresponding wild-type control were analyzed to characterize the structural and physicochemical properties of wheat starch. A transcriptomic analysis was used to analyze the differentially expressed genes (DEGs) involved in RS accumulation. The results showed that the RS content increased with grain development, along with the total starch content, but a larger increase was observed in the middle and later stages of grain filling. The X-ray diffraction peak intensity and relative crystallinity of starch exhibited the lowest and highest values at 10 days after anthesis, respectively. Regarding the thermal properties of starch, the peak temperature and conclusion temperature generally decreased with grain development; however, the enthalpy values showed no apparent regularity. Compared to control cultivar ZM22, the RS639 and RS683 lines with high RS contents showed high amylose contents and high relative crystallinity and a large proportion of 2.0~9.8 µm starch granules. Furthermore, the transcriptomics analysis revealed that the average relative expression of the glucan-branching enzyme (GBE) α-1,4 glucan phosphorylase (Pho) and starch synthase (SS) in ZM22 was 2.47-, 2.70-, and 2.56-fold higher than that in RS639, respectively; which indicates that the downregulation of the expression of genes encoding GBE, Pho, and SS in wheat grain promotes the accumulation of RS.