GW5-Like, a homolog of GW5, negatively regulates grain width, weight and salt resistance in rice

Grain size is an important determinant of yield potential in crops. We previously demonstrated that natural mutations in the regulatory sequences of qSW5/GW5 confer grain width diversity in rice. However, the biological function of a GW5 homolog, named GW5-Like(GW5 L), remains unknown. In this study, we report on GW5 L knockout mutants in Kitaake, a japonica cultivar(cv.)considered to have a weak gw5 variant allele that confers shorter and wider grains. GW5 L is evenly expressed in various tissues, and its protein product is localized to the plasma membrane. Biochemical assays verified that GW5 L functions in a similar fashion to GW5. It positively regulates brassinosteroid(BR) signaling through repression of the phosphorylation activity of GSK2. Genetic data show that GW5 L overexpression in either Kitaake or a GW5 knockout line, Kasaorf3(indica cv. Kasalath background), causes more slender, longer grains relative to the wild-type. We also show that GW5 L could confer salt stress resistance through an association with calmodulin protein OsCa M1-1. These findings identify GW5 L as a negative regulator of both grain size and salt stress tolerance, and provide a potential target for breeders to improve grain yield and salt stress resistance in rice.

Enhancing rice grain production by manipulating the naturally evolved cis-regulatory element-containing inverted repeat sequence of OsREM20

Grain number per panicle(GNP)is an important agronomic trait that contributes to rice grain yield.Despite its importance in rice breeding,the molecular mechanism underlying GNP regulation remains largely unknown.In this study,we identified a previously unrecognized regulatory gene that controls GNP in rice,Oryza sativa REPRODUCTIVE MERISTEM 20(OsREM20),which encodes a B3 domain transcription factor.Through genetic analysis and transgenic validation we found that genetic variation in the CArG box-containing inverted repeat(IR)sequence of the OsREM20 promoter alters its expression level and contributes to GNP variation among rice varieties.Furthermore,we revealed that the IR sequence regulates OsREM20 expression by affecting the direct binding of OsMADS34 to the CArG box within the IR sequence.Interestingly,the divergent pOsREM20IR and pOsREM20ΔIR alleles were found to originate from different Oryza rufipogon accessions,and were independently inherited into the japonica and indica subspecies,respectively,during domestication.Importantly,we demonstrated that IR sequence variations in the OsREM20 promoter can be utilized for germplasm improvement through either genome editing or traditional breeding.Taken together,our study characterizes novel genetic variations responsible for GNP diversity in rice,reveals the underlying molecular mechanism in the regulation of agronomically important gene expression,and provides a promising strategy for improving rice production by manipulating the cis-regulatory element-containing IR sequence.