Endonuclease Genes in Rice Are Involved in Phosphate Source Recycling by DNA Decay From Phosphate Deprivation

Enhancing phosphate use efficiency (PUE) has been a longstanding challenge in agriculture, as phosphate (Pi) is a crucial component of key organic molecules such as RNA, DNA, and ATP. In this study, we performed a comprehensive phylogenetic analysis of four rice and five Arabidopsis Endonuclease (ENDO) genes, which encode bifunctional nucleases capable of acting on both RNA and DNA. Our analysis revealed three distinct groups of ENDO genes: common, monocot-specific, and dicot-specific, indicating both functional conservation and diversification among monocot and dicot species. Interestingly, we found that only the monocot-specific group of rice ENDO genes exhibited differential regulation in response to P deficiency, a response not observed in Arabidopsis. Additionally, overexpression of OsPHR2, a central regulator of P homeostasis, resulted in increased DNA fragmentation and degradation, along with upregulation of OsENDO3 and OsENDO4. Transient expression assays further demonstrated that OsPHR2 activates both OsENDO3 and OsENDO4, suggesting that P-starved conditions trigger the expression of two OsPHR2-dependent rice ENDO genes. Overall, our findings suggest that OsENDO3 and OsENDO4 play a role in recycling P sources by regulating DNA decay under P deficient conditions. This insight could have significant implications for improving P use efficiency in agriculture, addressing a critical and enduring agricultural challenge.