| Summary: | Vacuolar invertase is involved in sugar metabolism and plays a crucial role in plant growth and development, thus regulating seed size. However, information linking vacuolar invertase and seed size in rice is limited. Here we characterized a small grain mutant <i>sg2</i> (grain size on chromosome 2) that showed a reduced in grain size and 1000-grain weight compared to the wild type. Map-based cloning and genetic complementation showed that <i>OsINV3</i> is responsible for the observed phenotype. Loss-of-function of <i>OsINV3</i> resulted in grains of smaller size when compared to the wild type, while overexpression showed increased grain size. We also obtained a T-DNA insertion mutant of <i>OsINV2</i>, which is a homolog of <i>OsINV3</i> and generated double knockout (<i>KO</i>) mutants of <i>OsINV2</i> and <i>OsINV3</i> using CRISPR/Cas9. Genetic data showed that <i>OsINV2</i>, that has no effect on grain size by itself, reduces grain length and width in the absence of <i>OsINV3</i>. Altered sugar content with increased sucrose and decreased hexose levels, as well as changes vacuolar invertase activities and starch constitution in <i>INV3<sup>KO</sup></i>, <i>INV2<sup>KO</sup></i>, <i>INV3<sup>KO</sup>INV2<sup>KO</sup></i> mutants indicate that <i>OsINV2</i> and <i>OsINV3</i> affect sucrose metabolism in sink organs. In summary, we identified <i>OsINV3</i> as a positive regulator of grain size in rice, and while <i>OsINV2</i> has no function on grain size by itself. In the absence of <i>OsINV3</i>, it is possible to detect a role of <i>OsINV2</i> in the regulation of grain size. Both <i>OsINV3</i> and <i>OsINV2</i> are involved in sucrose metabolism, and thus regulate grain size. Our findings increase our understanding of the role of <i>OsINV3</i> and its homolog, <i>OsINV2</i>, in grain size development and also suggest a potential strategy to improve grain yield in rice.
|
|---|
