Improving rice eating and cooking quality by coordinated expression of the major starch synthesis-related genes, SSII and Wx, in endosperm

Starch biosynthesis in cereal endosperms: An updated review over the last decade

“…Recent studies have found that some SSRGs that are weakly expressed in cereal endosperms nonetheless play significant roles in endosperm starch synthesis and quality formation ( Tian et al., 2009 ; Lee et al., 2017 ; Zeng et al., 2017 ). For example, knockdown or knockout of SSIIb ( SSII-2 ), which is expressed at a low level in the endosperm, suppressed the expression of SSIIa , SSIIb , and Wx , resulting in decreased AC, altered amylopectin CLD, and novel low-amylose rice with soft, transparent grains ( Li et al., 2018b ; Huang et al., 2021 ). Numerous mutation combinations with various starch properties can be isolated from different SSRG mutations, but only a few such combinations have been obtained, significantly limiting relevant studies ( Jeon et al., 2010 ).…”

“…An increase in grain AC may drastically reduce starch digestion rate and reduce eating and cooking quality; the inhibition of SBEIIb or SSIIIa led to an increase in AC and a reduction in grain yield ( Zhu et al., 2012 ; Zhou et al., 2016 ). Compared with SSRGs predominantly expressed in the endosperm and pleiotropic TFs, SSRGs with a relatively low level of expression in the endosperm appear to be more suitable for crop breeding because their mutations tend to cause moderate changes in starch synthesis ( Huang et al., 2021 ). Furthermore, fine-tuning of the expression or enzyme activity of SSRGs with predominant expression in the endosperm is also likely to be useful in developing elite cereal varieties with improved grain quality without compromising yield traits ( Huang et al., 2020b ; Xu et al., 2021 ).…”

Mining of Potential Gene Resources for Breeding Nutritionally Improved Maize

“…In rice, the repression of genes that encode isozymes SSI, SSIIa and SSIIIa via RNAi strongly influenced grain development, while repression of the other four SS encoding genes did not show any effect [ 17 ]. Another study on rice SS has also suggested that improved grain quality can only be achieved by coordinated downregulation of the expression of SSIIb and SSIIc, indicating a functional redundancy between SSIIb and SSIIc [ 18 ].…”

“…Studies on rice [ 10 , 11 ], wheat [ 12 ], barley [ 13 ], potatoes [ 14 , 15 ] and cassava [ 16 ] showed the content of Am was increased when the activity of SBEs was suppressed, supporting the notion that manipulation of SBE is an effective way to increase the Am content. The effect of SSs on starch synthesis has been investigated and confirmed in rice [ 17 , 18 ] and sweet potatoes [ 19 ]. Granule bound starch synthase (GBSS) binds specially to starch and maintains the unbranching state of Am while the Protein Targeting to Starch 1 (PTST1) participates in the localization of GBSS in Am.…”

Introgression Lines: Valuable Resources for Functional Genomics Research and Breeding in Rice (Oryza sativa L.)

“…For example, to improve the eating and cooking quality of Zhenshan 97 and its hybrid Shanyou 63, the Wx/Waxy gene region from Minghui 63, a restorer line with medium amylose content (AC), soft gel consistency (GC), and high gelatinization temperature (GT), was introgressed into Zhenshan 97B and then transferred into Zhenshan 97A ( Zhou et al, 2003 ). In recent years, the discovery of different alleles of Wx and ALK has provided more choices for rice grain quality improvement via gene introgression ( Chen et al, 2020 ; Huang et al, 2021 ; Zhang et al, 2021b ; Zhou et al, 2021 ). GS9 is an important gene for both grain shape and chalkiness, and appearance quality could be largely improved by developing an IL for this gene ( Zhao et al, 2018 , 2021 ).…”