Quantitative regulation of Waxy expression by CRISPR/Cas9‐based promoter and 5'UTR‐intron editing improves grain quality in rice

摘要

In cereal crops, grain starches are composed of differentproportions of amylose and amylopectin, which determine thecooking and eating qualities. The amylose synthesis is controlledby the Waxy (Wx) gene encoding a granule bound NDP-glucosestarch glucosyltransferase (Shure et al., 1983). In rice (Oryza sativaL.), the varied activities of natural Wx alleles regulate differentamylose contents (AC), gel consistency (GC) and pasting viscosityof grain starches; these factors together influence the grainappearance, cooking/eating quality and starch physical characters(Zhang et al., 2019). Wxa is a strong allele mainly distributing inindica (an O. sativa subspecies) cultivars producing high ACs(25%–30%) (Wang et al., 1995). While Wxb, presenting mainly injaponica (another subspecies) cultivars, is a weak allele producingmoderate ACs (15–18%) (Isshiki et al., 1998). Generally, ricegrains with higher ACs and lower GC values have poor eatingquality, while those with moderate ACs (15–20%) and higher GCvalues (60–80 mm) give better taste for most consumers. Usingthe successive backcrossing methods, Wxb can be introgressedinto indica varieties to improve the grain quality. However, thetraditional breeding methods are time consuming and difficult tobreak close linkage drags with undesirable traits.