The Harbinger transposon-derived gene PANDA epigenetically coordinates panicle number and grain size in rice.

Transposons significantly contribute to genome fractions in many plants. Although numerous transposon-related mutations have been identified, the evidence regarding transposon-derived genes regulating crop yield and other agronomic traits is very limited. In this study, we characterized a rice Harbinger transposon-derived gene called PANICLE NUMBER AND GRAIN SIZE (PANDA), which epigenetically coordinates panicle number and grain size. Mutation of PANDA caused reduced panicle number but increased grain size in rice, while transgenic plants overexpressing this gene showed the opposite phenotypic change. The PANDA-encoding protein can bind to the core polycomb repressive complex 2 (PRC2) components OsMSI1 and OsFIE2, and regulates the deposition of H3K27me3 in the target genes, thereby epigenetically repressing their expression. Among the target genes, both OsMADS55 and OsEMF1 were negative regulators of panicle number but positive regulators of grain size, partly explaining the involvement of PANDA in balancing panicle number and grain size. Moreover, moderate overexpression of PANDA driven by its own promoter in the indica rice cultivar can increase grain yield. Thus, our findings present a novel insight into the epigenetic control of rice yield traits by a Harbinger transposon-derived gene and provide its potential application for rice yield improvement.

NP and 9311 are excellent population parents for screening QTLs of potassium-efficient rice.

High and stable rice yields are critical to global food security, and potassium-deficient soils in East Asia have seriously limited rice production in the regions. It is feasible to screen potassium efficient quantitative trait locus(QTLs) from existing rice varieties to cope with rice production in potassium-deficient areas, and the selection of population parents is the key to locating major QTLs. After a long period of natural selection, potassium efficient rice varieties mainly exist in the region where the soil potassium level is low. The present study chose the representative twelve high-yielding rice varieties in east Asia, firstly, to measure plant height, fresh sheath weight, and fresh blade weight under hydroponic conditions. Based on the difference and consistency of the three parameters, NP as low potassium tolerant, and 9311 as low potassium sensitive rice variety were screened. We further analyzed the relative values of the six parameters of NP and 9311 treated with a culture medium containing different potassium (K+) concentrations and showed that the two varieties significantly differed in multiple low potassium concentrations. Meanwhile, we calculated the coefficient of variation of twelve rice varieties and most of those parameters reached a maximum at 4 mg/L K+, indicating that this concentration was suitable for screening potassium-efficient rice. We also measured the potassium content and the potassium-related traits in NP and 9311 tissues, and found that NP and 9311 significantly differed in potassium translocation. These differences may be responsible for the long-distance transport of potassium from the root to the aboveground part. In conclusion, we identified a pair of parents with significant differences in potassium translocation, which can be used to locate the relevant QTLs with high potassium efficiency to cope with the crisis of soil potassium deficiency in East Asia.