National Key Laboratory of Crop Genetic Improvement, Huazhong Agriculture University, Wuhan, 430070, China.
College of Agriculture, Yangtze University, Jingzhou, 434000, China.
Theor Appl Genet. 2020 Aug;133(8):2387-2399. doi: 10.1007/s00122-020-03606-z. Epub 2020 May 29.
SG3, an R2R3 MYB protein coding gene that tightly linked to a major QTLGS3, negatively regulates grain length while dependent on the status ofGS3in rice. It is often very difficult to isolate a minor QTL that is closely linked to a major QTL in rice. In this study, we focused on the isolation of a minor grain length QTL, small grain 3 (SG3), which is closely linked to the major QTL grain size 3 (GS3). The genetic effect of SG3 on grain length was dependent on GS3 status. Its genetic effect was larger in the presence of nonfunctional sg3 than functional SG3. A large number of near-isogenic F2 plants in which GS3 was fixed with nonfunctional alleles were developed to clone SG3. A gene encoding an R2R3 MYB domain transcriptional regulator was identified as the candidate gene for SG3. SG3 overexpression and knockdown plants showed shortened and elongated grains, respectively, which demonstrated that SG3 acts as a negative regulator of grain length. SG3 was preferentially expressed in panicles after flowering, and SG3 acted as a transcription activator. Comparative sequencing analysis identified a 12-bp insertion in the third exon of NYZ that led to a frameshift and resulted in a premature stop codon. The insertion/deletion was associated with grain length in the presence of functional GS3 in the indica subspecies. SG3 and GS3 were frequently in coupling phase in indica rice, making them good targets for the breeding of cultivars with short or long grains. The isolation of the SG3 MYB gene provides new gene resource and contributes to the regulatory network of grain length in rice.
SG3 是一个 R2R3 MYB 蛋白编码基因，与一个主要的 QTLGS3 紧密连锁，负调控粒长，同时依赖于水稻中 GS3 的状态。在水稻中，分离与主要 QTL 紧密连锁的微效 QTL 通常非常困难。在本研究中，我们专注于分离一个与主要粒长 QTLGS3 紧密连锁的微效粒长 QTL，即小粒 3（SG3）。SG3 对粒长的遗传效应依赖于 GS3 的状态。在非功能 sg3 存在的情况下，其遗传效应大于功能 SG3。我们开发了大量具有非功能等位基因固定的 GS3 的近等基因 F2 植物，以克隆 SG3。鉴定到一个编码 R2R3 MYB 结构域转录调节因子的基因作为 SG3 的候选基因。SG3 过表达和敲低植物分别表现出缩短和伸长的粒长，表明 SG3 作为粒长的负调控因子发挥作用。SG3 在开花后花穗中优先表达，并且作为转录激活因子发挥作用。比较测序分析鉴定到在 NYZ 的第三外显子中存在 12-bp 插入，导致移码和提前终止密码子。该插入/缺失与籼亚种中功能 GS3 存在时的粒长相关。SG3 和 GS3 在籼稻中经常处于偶联相位，使它们成为培育短粒或长粒品种的良好目标。SG3 MYB 基因的分离提供了新的基因资源，有助于水稻粒长的调控网络。
