Posttranslational Modification of Waxy to Genetically Improve Starch Quality in Rice Grain

Abstract

The waxy (Wx) gene, encoding the granule-bound starch synthase (GBSS), is responsible for amylose biosynthesis and plays a crucial role in defining eating and cooking quality. The waxy locus controls both the non-waxy and waxy rice phenotypes. Rice starch can be altered into various forms by either reducing or increasing the amylose content, depending on consumer preference and region. Low-amylose rice is preferred by consumers because of its softness and sticky appearance. A better way of improving crops other than downregulation and overexpression of a gene or genes may be achieved through the posttranslational modification of sites or regulatory enzymes that regulate them because of their significance. The impact of posttranslational GBSSI modifications on extra-long unit chains (ELCs) remains largely unknown. Numerous studies have been reported on different crops, such as wheat, maize, and barley, but the rice starch granule proteome remains largely unknown. There is a need to improve the yield of low-amylose rice by employing posttranslational modification of Wx, since the market demand is increasing every day in order to meet the market demand for low-amylose rice in the regional area that prefers low-amylose rice, particularly in China. In this review, we have conducted an in-depth review of waxy rice, starch properties, starch biosynthesis, and posttranslational modification of waxy protein to genetically improve starch quality in rice grains.

Keywords: GBSSI; amylose; posttranslational modification; rice; waxy.

Figure 1

Varieties of amylose rice regionally preferred by different countries. Classification of milled rice based on amylose content and the list of countries that preferred different varieties of amylose rice (created with BioRender.com).

Figure 2

“Main pathway of starch biosynthesis including sucrose synthesis, sucrose degradation and starch synthesis in rice” [8]. “FBP1, fructose-1,6-bisphophatase1; PGM, phosphoglucomutase; AGPase, ADP-glucose pryophosphorylase; PPi, pyrophosphate” [8]. For both gel consistency and amylose content, waxy (GBSSI, marked with a green star) serves as a vital/critical gene, but it has a minor influence on the temperature of gelatinization. The amylose and amylopectin circled in red color are very important in starch modification. Source: Sun et al. [8].