An abundant 17 kDa RNase, encoded by OsPR10a (also known as PBZ1), was purified from P_i-starved rice suspension-cultured cells. Biochemical analysis showed that the range of optimal temperature for its RNase activity was 40–70°C and the optimum pH was 5.0. Disulfide bond formation and divalent metal ion Mg²⁺ were required for the RNase activity. The expression of OsPR10a::GUS in transgenic rice was induced upon phosphate (P_i) starvation, wounding, infection by the pathogen Xanthomonas oryzae pv. oryzae (Xoo), leaf senescence, anther, style, the style-ovary junction, germinating embryo and shoot. We also provide first evidence in whole-plant system, demonstrated that OsPR10a-overexpressing in rice and Arabidopsis conferred significant level of enhanced resistance to infection by the pathogen Xoo and Xanthomona campestris pv. campestris (Xcc), respectively. Transgenic rice and Arabidopsis overexpressing OsPR10a significantly increased the length of primary root under phosphate deficiency (-P_i) condition. These results showed that OsPR10a might play multiple roles in phosphate recycling in phosphate-starved cells and senescing leaves, and could improve resistance to pathogen infection and/or against chewing insect pests. It is possible that P_i acquisition or homeostasis is associated with plant disease resistance. Our findings suggest that gene regulation of OsPR10a could act as a good model system to unravel the mechanisms behind the correlation between P_i starvation and plant-pathogen interactions, and also provides a potential application in crops disease resistance.

Overexpression of a constitutively active truncated form of OsCDPK1 (OEtr) in rice produced smaller seeds, but a double-stranded RNA gene-silenced form of OsCDPK1 (Ri) yielded larger seeds, suggesting that OsCDPK1 plays a functional role in rice seed development. In the study presented here, we propose a model in which OsCDPK1 plays key roles in negatively controlling the grain size, amylose content, and endosperm appearance, and also affects the physicochemical properties of the starch. The dehulled transgenic OEtr grains were smaller than the dehulled wild-type grains, and the OEtr endosperm was opaque and had a low amylose content and numerous small loosely packed polyhedral starch granules. However, the OEtr grain sizes and endosperm appearances were not affected by temperature, which ranged from low (22 °C) to high (31 °C) during the grain-filling phase. In contrast, the transgenic Ri grains were larger, had higher amylose content, and had more transparent endosperms filled with tightly packed polyhedral starch granules. This demonstrates that OsCDPK1 plays a novel functional role in starch biosynthesis during seed development and affects the transparent appearance of the endosperm. These results improve our understanding of the molecular mechanisms through which the grain-filling process occurs in rice.

The rice pathogenesis-related protein OsPR10a was scarcely expressed in OsCDPK1-silenced (Ri-1) rice, which was highly sensitive to pathogen infection. After inoculating the leaves with bacterial blight (Xanthomonas oryzae pv. oryzae; Xoo), we found that the expression of OsPR10a was up- and down-regulated in OEtr-1 (overexpression of the constitutively active truncated form of OsCDPK1) and Ri-1 rice plants, respectively. OsPR10a and OsCDPK1 showed corresponding expression patterns and were up-regulated in response to the jasmonic acid, salicylic acid and Xoo treatments, and OsPR1 and OsPR4 were significantly up-regulated in OEtr-1. These results suggest that OsCDPK1 may be an upstream regulator involved in rice innate immunity and conferred broad-spectrum of disease resistance. Following the Xoo inoculation, the OEtr-1 and Ri-1 seedlings showed enhanced and reduced disease resistance, respectively. The dihybrid rice Ri-1/OsPR10a-Ox not only bypassed the effect of OsCDPK1 silencing on the susceptibility to Xoo but also showed enhanced disease resistance and, consistent with Ri-1 phenotypes, increased plant height and grain size. Our results reveal that OsCDPK1 plays novel key roles in the cross-talk and mediation of the balance between stress response and development and provides a clue for improving grain yield and disease resistance simultaneously in rice.

TOPLESS (TPL) and TOPLESS-Related (TPR) corepressors are key regulatory proteins that interact with a variety of transcription factors to form specific complexes, thereby modulating a wide range of signaling pathways and metabolic processes. This study explored the function of the rice TPR gene OsTPR1. Transgenic rice lines overexpressing OsTPR1 (OsTPR1-Ox) exhibited reduced lateral root density, whereas OsTPR1 RNA interference lines (OsTPR1-Ri) showed increased lateral root density. To gain further insight, these transgenic lines were crossed with the DR5::GUS auxin reporter line. In 7-day-old seedlings, lateral root formation occurred in the differentiation zone of seminal roots, with GUS staining prominently localized in the lateral root primordia of the DR5::GUS/OsTPR1-Ri line. Similar results were observed in 45-day-old seedlings, where the DR5::GUS/OsTPR1-Ri line exhibited stronger GUS staining and a higher number of lateral roots in the crown root differentiation zones. In contrast, the DR5::GUS/OsTPR1-Ox line showed weaker GUS signals and fewer lateral roots. Additionally, the expression levels of several auxin efflux transporter genes encoding PIN-FORMED (PIN) proteins, including OsPIN1a, OsPIN1b, OsPIN1c, OsPIN2, and OsPIN5a, were increased in the OsTPR1-Ri line but decreased in the OsTPR1-Ox line. These results suggest that OsTPR1 also modulates the expression of multiple OsPIN genes, thereby potentially influencing auxin responses and lateral root development. Beyond root development, OsTPR1 overexpression led to a significant increase in tiller angle and a delay in flowering time, whereas OsTPR1-Ri plants exhibited earlier flowering. These findings indicate that OsTPR1 acts as a negative regulator of the auxin response, with its overexpression leading to reduced auxin sensitivity and altered plant architecture. Our results show that OsTPR1 modulates lateral root development, tiller angle, and flowering time, contributing to the coordinated growth and development in rice.