Deciphering the Role of Waxy Gene Mutations in Enhancing Rice Grain Quality.

Amylose content (AC) stands as a pivotal determinant of rice grain quality, primarily governed by the Waxy gene (Wx). The allelic variation within this gene, particularly the presence of the Wxmp allele derived from the ancestral Wxmq allele, significantly influences AC and is prevalent among soft japonica rice varieties in southern China. Although both alleles are associated with lower AC, there remains a paucity of detailed understanding regarding the interplay between specific functional single nucleotide polymorphisms (SNPs) within these alleles and the overarching rice grain quality. To investigate this, we engineered three distinct transgenic rice lines, each harboring the Wxmp, Wxmq, or Wxb-5c alleles in the background of the glutinous rice cultivar Nip(wx). This suite of transgenic rice lines showcased varying degrees of grain transparency inversely correlated to AC, which in turn influenced other physicochemical properties of the rice grains, such as taste value of cooked rice, gel consistency, and starch pasting properties. Additionally, analyses of gene expression and enzyme activity revealed that the functional SNPs, Ex4-53G to A and Ex5-53T to C, lead to a decline in the activity of granule-bound starch synthase I (GBSSI) without altering expression levels.

The Physicochemical Properties of Starch Are Affected by Wxlv in Indica Rice.

Amylose largely determines rice grain quality profiles. The process of rice amylose biosynthesis is mainly driven by the waxy (Wx) gene, which also affects the diversity of amylose content. The present study assessed the grain quality profiles, starch fine structure, and crystallinity characteristics of the near-isogenic lines Q11(Wxlv), NIL(Wxa), and NIL(Wxb) in the indica rice Q11 background containing different Wx alleles. Q11(Wxlv) rice contained a relatively higher amylose level but very soft gel consistency and low starch viscosity, compared with rice lines carrying Wxa and Wxb. In addition, starch fine structure analysis revealed a remarkable decrease in the relative area ratio of the short amylopectin fraction but an increased amylose fraction in Q11(Wxlv) rice. Chain length distribution analysis showed that Q11(Wxlv) rice contained less amylopectin short chains but more intermediate chains, which decreased the crystallinity and lamellar peak intensity, compared with those of NIL(Wxa) and NIL(Wxb) rice. Additionally, the starches in developing grains showed different accumulation profiles among the three rice lines. Moreover, significant differences in starch gelatinization and retrogradation characteristics were observed between near-isogenic lines, which were caused by variation in starch fine structure. These findings revealed the effects of Wxlv on rice grain quality and the fine structure of starch in indica rice.

Progress on inheritance and gene cloning for rice grain quality in Jiangsu province.

In China, rice (Oryza sativa L.) is a major cereal crop of great importance maintaining the food security and sustainable agricultural development. Jiangsu is one of the main provinces for rice production. After more than 40 years of development, the yield and quality of rice grain have made great progress. Rice grain quality is a complex trait involving production, processing, marketing and consumption of the grain. In this review, we summarize the progress on the genetic basis of main grain quality traits in the rice variety breeding in Jiangsu province and point out the achievement of each milestone. With a focus on the genetic regulation of grain appearance, eating and cooking quality and nutritional quality, we describe the classic genetic rules and molecular basis of rice grain quality traits and review the function of major genes that regulate corresponding traits. The genetics and improvement of grain quality achieved in Jiangsu province was highlighted on the domestic and international rice breeding programs. In particular, with the advance of breeding conception in terms of functional genomics and genetic regulatory networks, the specific molecular design for grain quality improvement will be the future direction of rice genetic breeding program of Jiangsu Province.

Genetic Dissection and Functional Differentiation of ALKa and ALKb, Two Natural Alleles of the ALK/SSIIa Gene, Responding to Low Gelatinization Temperature in Rice.

BACKGROUND: ALK is the key gene controlling rice gelatinization temperature (GT), which is closely associated with the eating and cooking quality (ECQ) in rice (Oryza sativa L.). To date, at least three ALK alleles are thought to be responsible for the diversity of GT among rice cultivars. The ALKc/SSIIai allele with high activity of the soluble starch synthase IIa (SSIIa) controls high GT, but the accurate functional difference between ALKa and ALKb alleles, both controlling low GT, is not clearly elucidated. Thus, we generated rice near-isogenic lines (NILs) by introducing different ALK alleles into the japonica cultivar Nipponbare (Nip) to clarify the discrepant effects of the two low-GT ALK alleles. RESULTS: The results showed that the function of two low-GT alleles (ALKa and ALKb) was different, and a much lower GT was observed in NIL(ALKb) rice grains compared with that of Nip(ALKa). Moreover, the starches of NIL(ALKb) grains had a higher degree of branching, higher setback, consistence and higher cool pasting viscosity than those of Nip(ALKa). The lower expression level of ALKb, compared with ALKa, resulted in depleted intermediate chains and increased short chains of amylopectin, thus affected the thermal and pasting properties of NILs' grains. Also, the data revealed both low-GT alleles were mainly found in temperate japonica, but more ALKb was found in other subpopulations such as indica as compared to ALKa. CONCLUSIONS: Overall, all the results suggested that the function between two low-GT alleles was different, and the distribution of ALKb was much wider than that of ALKa among the subpopulations of cultivated rice.

Changes in the physicochemical properties and starch structures of rice grains upon pre-harvest sprouting.

In rice production, pre-harvest sprouting (PHS) of late ripening seeds is one of the most serious quality defects in rice grain quality. In the present study, PHS impact was investigated by examining the physicochemical properties, eating and cooking quality (ECQ) of rice grain. Four rice cultivars suffering from PHS had impaired ECQ, reduced apparent amylose content, and decreased total starch content, with an increase in total protein content. The viscosity of flours and starches prepared from the PHS grains was significantly reduced. Starch molecular structure analysis also showed remarkable decreases in the short chains of amylopectin, long amylose chains and reduced starch crystallinity of the PHS grains. Moreover, the PHS native starch tended to have low starch digestibility. This provides useful information for understanding the effects of PHS on white rice grain quality as well as on starch fine structure and its physicochemical properties.