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OsVIN2, a vacuolar invertase, affects grain size and yield by altering sugar composition, transport, and starch accumulation in rice. Grain size, a major determinant of rice yield, is influenced by many developmental and environmental factors. Sugar metabolism plays vital roles in plant development. However, the way in which sugar metabolism affects rice grain size remains largely elusive. In this study, we characterized the small grain-size rice mutant sgs1. Histological analyses showed that reduced spikelet hull and endosperm size results from decreased cell size rather than cell number. Map-based cloning and complementation tests revealed that a DaiZ7 transposon insertion in a vacuolar invertase gene OsVIN2 is responsible for the mutant phenotype. Subcellular distribution and biochemical analysis indicated that OsVIN2 is located in the vacuolar lumen, and that its sucrose hydrolysis activity is maintained under acidic conditions. Furthermore, an altered sugar content with increased sucrose and decreased hexose levels, as well as changes in invertase and sucrose synthase activities, sugar transport gene expression, and starch constitution in sgs1 implies that OsVIN2 affects sucrose metabolism, including sugar composition, transport, and conversion from the source to the sink organs. Collectively, OsVIN2 is involved in sugar metabolism, and thus regulates grain size; our findings provide insights into grain development and also suggest a potential strategy to improve grain quality and yield in rice.

EH7/Ghd7 interacts with DTH8, and regulates heading date by controlling the expression of Ehd1 in rice. Heading date, or flowering time, an important agronomic trait, influences regional adaptability and yield of crops. Many genes related to heading date in rice have been identified, and a preliminary regulatory network has been established, but the relationships between proteins involved are poorly understood. We identified a flowering suppressor EH7 (Early heading 7) that represses flowering under long-day (LD) conditions. The eh7 allele caused earlier heading, shorter plant height and less grain per main panicle than did the wild type (WT), but the tiller number and 1000-grain weight were not significantly affected under natural long-day conditions. Biochemical assays showed that EH7 interacts with DTH8. Quantitative PCR showed that EH7 inhibited heading date by downregulating the expression of Ehd1, Hd3a and RFT1. We propose that EH7 interacts with DTH8 to control flowering time by regulating the expression of Ehd1, Hd3a and RFT1.

WSL3 encodes β-ketoacyl-CoA reductase (KCR) in rice, in a similar way to YBR159w in yeast, and is essential for VLCFA biosynthesis and leaf wax accumulation. Cuticular waxes on plant surfaces limit non-stomatal water loss, protect plants against deposits of dust and impose a physical barrier to pathogen infection. We identified a wax-deficient mutant of rice, wax crystal-sparse leaf 3 (wsl3), which exhibits a pleiotropic phenotype that includes reduced epicuticular wax crystals on the leaf surface and altered wax composition. Map-based cloning demonstrated that defects in the mutant were caused by two adjacent single-nucleotide changes in a gene encoding β-ketoacyl-CoA reductase (KCR) that catalyzes the second step of the fatty acid elongation reaction. The identity of WSL3 was further confirmed by genetic complementation. Transient assays of fluorescent protein-tagged WSL3 in tobacco protoplasts showed that WSL3 localizes to the endoplasmic reticulum, the compartment of fatty acid elongation in cells. Quantitative PCR and histochemical staining indicated that WSL3 is universally expressed in tissues. RNA interference of WSL3 caused a phenotype that mimicked the wsl3 mutant. Very long-chain fatty acids (VLCFAs) 20:0 and 22:0, or 20:1Δ11 and 22:1Δ13, were detected when WSL3 and Arabidopsis fatty acid elongation 1 (FAE1) were co-expressed in a yeast ybr159wΔ mutant strain. Our results indicated that WSL3 affects rice cuticular wax production by participating in VLCFA elongation.