The deployment of heterosis in the form of hybrid rice varieties has boosted grain yield. However, improvements in grain quality still remains a challenge, as this trait is a complex trait that is multiplicatively determined by appearance, cooking and eating quality, etc., all of which are controlled by quantitative trait loci (QTLs) and influenced by environmental changes. Despite a great deal of research effort, only a small number of relevant genes have been identified thus far.
 

Prof. FU Xiangdong’s group at the Institute of Genetics and Developmental Biology (IGDB), Chinese Academy of Sciences, has identified a quantitative trait locus for rice grain quality, qGW7, reflects allelic variation of GW7, a gene encoding a TONNEAU1-recruiting motif protein with similarity to C-terminal motifs of the human centrosomal protein CAP350.
 

Upregulation of GW7 expression was correlated with the production of more slender grains, as a result of increased cell division in the longitudinal direction and decreased cell division in the transverse direction. OsSPL16 (GW8), a SBP-domain transcription factor that regulates grain width, bound directly to the GW7 promoter and repressed its expression. The presence of a semidominant GW7TFA allele from tropical japonica rice was associated with higher grain quality without the yield penalty imposed by the Basmati gw8 allele.
 

Their findings provide new insights into the role of SBP-domain transcription factors in the spatial control of plant cell division. The expression of OsSPL16 is already known to be controlled by OsmiR156, thus, manipulation of the OsmiR156-OsSPL16-GW7 regulatory module opens the way to breeding simultaneously for higher grain yield and better grain quality in rice.

The paper has been published online in Nature Genetics on July 6, 2015. This work is supported by grants from the National Natural Science Foundation of China, the Ministry of Science and Technology of China  and the National Special Project of China.

Contact:
Dr. FU Xiangdong
Institute of Genetics and Developmental Biology, Chinese Academy of Sciences,
Beijing China
Email: xdfu@genetics.ac.cn

Figure 1. GW7TFA allele enhanced rice grain appearance quality and better quality as well as the advantage in grain yield over the Basmati gw8 allele. (A) Grain shape. Scale bar, 2 mm. (B) Ratio of grain length to width. Data are shown as means ± s.e.m. (n = 60). Student’s t test was used to generate the P value. (C) 1,000-grain weight. Data are shown as means ± s.e.m. (n = 180). (D) Overall grain yield per plant. Data are shown as means ± s.e.m. (n = 300). The presence of the same lowercase letter denotes a non-significant difference between the means (P > 0.05; C and D). All phenotypic data were measured from paddy-grown plants under normal cultivation conditions. (Image by IGDB)