Improving Agricultural Traits While Maintaining High Resistant Starch Content in Rice

Abstract

Background Resistant starch (RS) is beneficial for human health. Loss of starch branching enzyme IIb (BEIIb) increases the proportion of amylopectin long chains, which greatly elevates the RS content. Although high RS content cereals are desired, an increase in RS content is often accompanied by a decrease in seed weight. To further increase the RS content, genes encoding active-type starch synthase (SS) IIa, which elongates amylopectin branches, and high expression-type granule-bound SSI (GBSSI), which synthesizes amylose, were introduced into the be2b mutant rice. This attempt increased the RS content, but further improvement of agricultural traits was required because of a mixture of indica and japonica rice phonotype, such as different grain sizes, flowering times, and seed shattering traits. In the present study, the high RS lines were backcrossed with an elite rice cultivar, and the starch properties of the resultant high-yielding RS lines were analyzed. Results The seed weight of high RS lines was greatly improved after backcrossing, increasing up to 190% compared with the seed weight before backcrossing. Amylopectin structure, gelatinization temperature, and RS content of high RS lines showed almost no change after backcrossing. High RS lines contained longer amylopectin branch chains than the wild type, and lines with active-type SSIIa contained a higher proportion of long amylopectin chains compared with the lines with less active-SSIIa, and thus showed higher gelatinization temperature. Although the RS content of rice varied with the cooking method, those of high RS lines remained high after backcrossing. The RS contents of cooked rice of high RS lines were high (27–35%), whereas that of the elite parental rice was considerably low (< 0.7%). The RS contents of lines with active-type SSIIa and high-level GBSSI expression in be2b or be2b ss3a background were higher than those of lines with less-active SSIIa. Conclusions The present study revealed that backcrossing high RS rice lines with elite rice cultivars could increase the seed weight, without compromising the RS content. It is likely that backcrossing introduced loci enhancing seed length and width as well as loci promoting early flowering for ensuring an optimum temperature during RS biosynthesis.

Dynamics of starch formation and gene expression during grain filling and its possible influence on grain quality

“…Similar changes in amylopectin were observed in BEIIb CRISPR/Cas9 mutant of indica rice which has higher number of branches with DP 6, 7 and > 25 and lower number of chains with DP 9–24 leading to increased gelatinization temperature by 6 °C and increased amylose content by 7% 49 . Absence of BEIIb decreased the short chain number and increased the long chain number simultaneously 50 . In this study, SBEI expression was noted in all the varieties.…”

Three Starch Synthase IIa (SSIIa) Alleles Reveal the Effect of SSIIa on the Thermal and Rheological Properties, Viscoelasticity, and Eating Quality of Glutinous Rice

“…The SSIIa and wx genotypes of rice lines used in this study are summarized in Table 1 . IR36 is known to possess the Wx a (or GBSS1 ) allele [ 3 ], whereas Akita 63 and Kinmaze, the parental line of EM204, are known to possess the Wx b (or gbss1 L ) genotype [ 3 , 39 ]; the Wx a and Wx b alleles can be distinguished from each other based on nucleotide polymorphisms in the first intron of the Wx gene [ 40 ]. These results show that rice lines generated in this study possess the expected genotypes.…”

Starch Quality Matrix (SQM): An Analytical Model for Predicting Resistant Starch (RS) in Rice (Oryza sativa.L)

“…This might be because long amylopectin chains contribute towards more crystalline structure due to an increase in hydrogen bonds developed among the chains and thus increase the resistance to enzymatic hydrolysis (Sasaki et al 2009). A recent study has also shown that RS content in raw rice our is directly proportional to the content of amylose and long amylopectin chains (Miura et al 2022). It can be postulated that long amylopectin branches and amylose interact with each other during retrogradation to form imperfect helices, which prevents degradation by digestive enzymes and serves as RS2 and RS3.…”