Heebak Choi

Phosphorus (P) management has long been a challenge in agriculture, particularly improving P use efficiency (PUE) in crop plants, including rice. Although several studies have documented enhanced PUE in rice varieties, the underlying molecular mechanisms remain poorly understood, hindering crop engineering efforts. In this study, we expressed the rice ribonuclease 1 (OsRNS1) gene, which encodes a Class I monocot-specific ribonuclease, throughout the root under P deficiency, which was confirmed via green fluorescent protein and histochemical β-glucuronidase assays. Notably, the OsRNS1 protein localized in the cell wall and endoplasmic reticulum. Overexpression of OsRNS1 promoted ribosomal RNA (rRNA) degradation and PUE, while knockout of OsRNS1 reduced rRNA degradation. Moreover, OsRNS1 overexpression, driven by a root-preferred promoter, enhanced tolerance to P-deficiency stress compared with the wild type. OsRNS1 was regulated by the rice PHOSPHATE STARVATION RESPONSE 2 protein, and changes in OsRNS1 transcript levels influenced the expression of other acid phosphatase and phosphate transporter genes. Collectively, these findings indicate that OsRNS1, a P deficiency-induced ribonuclease, regulates P homeostasis via rRNA degradation during P-deficiency stress. This molecular mechanism of P-deficiency tolerance holds promise for biotechnological applications aimed at developing rice varieties with improved PUE.

The rice (Oryza sativa) PSEUDO-ETIOLATION IN LIGHT (OsPEL) microProtein family members function as dominant-negative regulators of chloroplast development and are conserved among land plants. Knockout of all 3 OsPEL genes enhanced plant greening traits and was accompanied by leaf anatomical modifications associated with chloroplast-enriched bundle sheath cells in rice. These phenotypic changes correlated with increased CO2 assimilation efficiency and yield. OsPEL1 specifically interacts with key positive regulators of photosynthesis, the rice GOLDEN2-LIKE (OsGLK) transcription factors and the PHOTOSYSTEM I ASSEMBLY 2 (OsPSA2) chaperone. OsPEL1 inhibits these regulators by sequestering OsGLK1 and OsPSA2 in the cytoplasm, which prevents their proper localization to the nucleus and chloroplast, respectively. Supported by RNA-seq evidence of transcriptional homeostasis in greening-related genes, we reveal a multilayered regulatory mechanism and identify the OsPEL family as a promising target for crop improvement.

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 O sENDO4 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.

GOLDEN2‐LIKE (GLK) transcription factors belong to the GARP superfamily and are known as major positive regulators of greening in various plants, including Arabidopsis, rice, maize, tomato, and moss. Recent studies have reported many GLK downstream targets and binding partners. This revealed the breadth of GLK‐related downstream pathways and its multiplexed‐regulatory system beyond greening regulation. To evaluate the complexity of the molecular mode of action of GLKs, here we summarize the current knowledge of the interactions from promoters of direct GLK downstream target genes involved in chlorophyll biosynthesis, photosystem I, photosystem II, catechin biosynthesis, flowering, and abscisic acid signaling, and proteins that directly bind to GLKs, including kinases, E3 ligases, repressors of GLK activity, histone deacetylases, transcriptional coregulators, and transcription factors. This overview of GLK‐related pathways supports the pleiotropic function of GLKs as core regulators of a multi‐regulatory system involving plant greening and other phenotypes.