Identifying genes involved in folate accumulation is critical for elucidating the regulatory mechanisms of folate metabolism and breeding folate-rich crops. Here, a natural A-to-G variation at the 682nd bp is identified in the coding sequence of an identified plant gene glutamate formiminotransferase (GFT) in maize, leading to a glycine-to-asparagine substitution at the 228th in the protein sequence and contributing to the variation of folate accumulation in mature seeds of a maize inbred line population. This gene encodes a protein highly similar to the formiminotransferase domain of mammalian formiminotransferase cyclodeaminase. In vitro biochemical analysis of this protein reveals an activity of triggering 5-methyl-tetrahydrofolate (5-M-THF)-to-MeFox conversion, other than exerting an activity of formiminotransferase in mammals. Loss of ZmGFT function triples 5-M-THF levels, and overexpression of G-allele-carrying ZmGFT boosts the metabolic flow toward MeFox. Functional conservation of GFT is validated in rice and Arabidopsis. The asparagine-to-glycine substitution enhances 5-M-THF-to-MeFox conversion, as demonstrated by in vitro assays and in silico analyses. The functional characterization of the GFT gene has uncovered a new metabolic fate of 5-M-THF, apart from a C1 donor for methionine synthesis, in plants, and a distinct activity from its mammalian ortholog. The natural variation identified is useful for breeding folate-fortified maize varieties.

Hybrid rice technology has been used for more than 50 years, and eating and cooking quality (ECQ) has been a major focus throughout this period. Waxy (Wx) and alkaline denaturation (ALK) genes have received attention owing to their pivotal roles in determining rice characteristics. However, despite significant effort, the ECQ of restorer lines (RLs) has changed very little. By contrast, obvious changes have been seen in inbred rice varieties (IRVs), and the ECQ of IRVs is influenced by Wx, which reduces the proportion of Wxa and increases the proportion of Wxb, leading to a decrease in amylose content (AC) and an increase in ECQ. Meanwhile, ALK is not selected in the same way. We investigated Wx alleles and AC values of sterile lines of female parents with the main mating combinations in widely used areas. The results show that almost all sterile lines were Wxa-type with a high AC, which may explain the low ECQ of hybrid rice. Analysis of hybrid rice varieties and RLs in the last 5 years revealed serious homogenisation among hybrid rice varieties.

Six rice cultivars with similarly high amylose contents but significant differences in resistant starch (RS) contents were employed to investigate factors affecting rice starch digestibility. Results of scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction analyses revealed that the enzymolysis resistance and high gelatinization temperature (GT) of the starch granules were the main reasons for the different starch digestibilities. Furthermore, starch fine structure analysis showed that RS content has a positive correlation with intermediate chain amylopectin (DP 13-24) content and a negative correlation with short chain amylopectin (DP 6-12) content. Moreover, under normal cooking conditions, some starch granules within the endosperm do not gelatinize completely due to the high GT of the starch, leading to a lower starch digestibility. Overall, this work provides useful information for understanding the effects of starch fine structure as well as GT on starch digestibility.

Rice grain quality is a complex trait that includes processing, appearance, eating, cooking, and nutrition components. The amylose content (AC) in the rice endosperm affects the eating and cooking quality along with the appearance of milled rice. In this study, four indica rice varieties with different ACs were used to study the factors affecting endosperm transparency along with the physical and chemical characteristics and eating quality of translucent endosperm varieties. Endosperm transparency was positively correlated with water content and negatively correlated with the cumulative area of cavities within starch granules. The indica landrace 28Zhan had a translucent endosperm and exhibited good taste. Based on starch fine structure analysis, long-chain amylopectin and the B2 chain of amylopectin might be major contributors to the good taste and relatively slow digestion of this landrace.

以4个具有相似的高直链淀粉含量水稻品种为试验材料,分析其淀粉和米粉的消化特性以及影n向消化特性的因素.结果 表明:相对于其他2个品种,MRX和ZXM的米粉和淀粉的酶解消化程度最低;所有品种水稻基本理化特性如表观直链淀粉含量、胶稠度、总淀粉以及蛋白质含量等对淀粉的消化特性无实质影响;不同品种间淀粉消化特性差异主要是由淀粉粒的结构差异引起的,MRX和ZXM淀粉粒在酶解消化过程中较为稳定,不易被酶侵蚀而破碎;其糊化温度和热焓值均显著高于其他2个品种,可能与其支链淀粉具有较高比例的短支链(DP 12-24)有关.

Folate deficiency is a global health problem. Biofortification has been considered a cost-effective means to tackle this problem. Here, we describe the genetic cloning and functional identification of a previously uncharacterised plant protein, designated as CTM, which functions as an enzyme in folate metabolism. Plant CTMs are capable of catalysing 5-methyl-tetrahydrofolate to MeFox, a pyrazino-s-triazine derivative of 4α-hydroxy-5-methyl-tetrahydrofolate. The natural asparagine-to-glycine substitution caused by an A-to-G single nucleotide variation in maize CTM enhances its enzymatic activity, as demonstrated by in vitro enzymatic assays and in silico analyses using a maize CTM structure model based on a monomeric sorghum CTM crystal. Loss of the CTM function led to accumulation of 5-methyl-tetrahydrofolate, and overexpression of the maize CTM carrying the G-allele boosted the metabolic flow towards MeFox, and showed no negative impacts on plant growth. Our results suggest that CTM, which has evolved 5-methyl-tetrahydrofolate-to-MeFox converting activity in plants, could be valuable for developing folate-biofortified crops to provide an alternative to the challenge presented by the global folate deficiency.

The gelatinization temperature (GT) of endosperm starch influences rice eating and the cooking quality (ECQ). ALK encoding soluble starch synthase IIa (SSIIa) is the major gene determining grain GT in rice. Herein, we identified a spontaneous ALK mutant named ALK(d), which resulted from a G/T single-nucleotide polymorphism (SNP) in exon 1 of the ALK(c) allele from the high-GT indica rice cultivar. Compared with grains from the ALK(c) near-isogenic line (NIL), NIL(ALK(d)) grains exhibited a high GT (2.3 degrees C) and improved retrogradation properties. The NIL(ALKa) grain starch contained an increased proportion of amylopectin intermediate chains (DP 13-24) at the expense of short chains (DP < 12), resulting in enhancements in both the crystallinity and the lamellar peak intensity compared with low-GT rice grains. Moreover, both NIL(ALK(d)) and NIL(ALK) grains also featured a significantly lower apparent amylose content (AAC), harder gel consistency (GC), higher pasting curve, and poorer taste values in comparison to Nip(ALK(d)) grains. Taken together, this work provides novel insights underlying the allelic variation of the ALK gene in rice.

Identification of grain shape determining genes can facilitate breeding of rice cultivars with optimal grain shape and appearance quality. Here, we identify GS9 (Grain Shape Gene on Chromosome 9) gene by map-based cloning. The gs9 null mutant has slender grains, while overexpression GS9 results in round grains. GS9 encodes a protein without known conserved functional domain. It regulates grain shape by altering cell division. The interaction of GS9 and ovate family proteins OsOFP14 and OsOFP8 is modulated by OsGSK2 kinase, a key regulator of the brassinosteroids signaling pathway. Genetic interaction analysis reveals that GS9 functions independently from other previously identified grain size genes. Introducing the gs9 allele into elite rice cultivars significantly improves grain shape and appearance quality. It suggests potential application of gs9, alone or in combination with other grain size determining genes, in breeding of rice varieties with optimized grain shape.

为改良当下我国南方地区杂交籼稻稻米蒸煮食味品质普遍较差的现状，本研究利用分子标记辅助选择的方法，分别构建了籼型杂交稻组合天优3611双亲天丰B 和3611携带 Wxin和Wxb的近等基因系，拟通过分析不同近等基因系杂交组合对杂交稻米品质改良的效应来明确杂交稻稻米品质改良的最佳Wx等位基因组合。研究结果表明，不同近等基因系的农艺性状与受体亲本基本接近。而导入的Wx等位基因对近等基因系稻米品质改良显著。构建了携带不同Wx等位基因近等基因系的杂交组合并对这些杂交组合稻米的品质进行了分析，发现，Wxin/Wxin,Wxa/Wxb和Wxb/Wxb组合对杂交稻米的品质改良明显。