A B-box transcription factor OsBBX17 regulates saline-alkaline tolerance through the MAPK cascade pathway in rice.

Rice OsBBX17 encodes a B-box zinc finger transcription factor in which the N-terminal B-box structural domain interacts with OsMPK1. In addition, it directly binds to the G-box of OsHAK2 and OsHAK7 promoters and represses their transcription. Under saline-alkaline conditions, the expression of OsBBX17 was inhibited. Meanwhile, activation of the OsMPK1-mediated mitogen-activated protein kinase cascade pathway caused OsMPK1 to interact with OsBBX17 and phosphorylate OsBBX17 at the Thr-95 site. It reduced OsBBX17 DNA-binding activity and enhanced saline-alkaline tolerance by deregulating transcriptional repression of OsHAK2 and OsHAK7. Genetic assays showed that the osbbx17-KO had an excellent saline-alkaline tolerance, whereas the opposite was in OsBBX17-OE. In addition, overexpression of OsMPK1 significantly improved saline-alkaline tolerance, but knockout of OsMPK1 caused an increased sensitivity. Further overexpression of OsBBX17 in the osmpk1-KO caused extreme saline-alkaline sensitivity, even a quick death. OsBBX17 was validated in saline-alkaline tolerance from two independent aspects, transcriptional level and post-translational protein modification, unveiling a mechanistic framework by which OsMPK1-mediated phosphorylation of OsBBX17 regulates the transcription of OsHAK2 and OsHAK7 to enhance the Na+ /K+ homeostasis, which partially explains light on the molecular mechanisms of rice responds to saline-alkaline stress via B-box transcription factors for the genetic engineering of saline-alkaline tolerant crops.

Phosphorylation of OsRbohB by the protein kinase OsDMI3 promotes H2O2 production to potentiate ABA responses in rice.

In rice, the Ca2+/calmodulin-dependent protein kinase OsDMI3 is an important positive regulator of abscisic acid (ABA) signaling. In ABA signaling, H2O2 is required for ABA-induced activation of OsDMI3, which in turn increase H2O2 production. However, how OsDMI3 regulates H2O2 production in ABA signaling remains unknown. Here we show that OsRbohB is the main NADPH oxidase involved in ABA-induced H2O2 production and ABA-mediated physiological responses. OsDMI3 directly interacts with and phosphorylates OsRbohB at Ser-191, which is OsDMI3-mediated site-specific phosphorylation in ABA signaling. Further analyses revealed that OsDMI3-mediated OsRbohB Ser-191 phosphorylation positively regulates the activity of NADPH oxidase and the production of H2O2 in ABA signaling, thereby enhancing the sensitivity of seed germination and root growth to ABA and plant tolerance to water stress and oxidative stress. Moreover, we discovered that the OsDMI3-mediated OsRbohB phosphorylation and H2O2 production is dependent on the sucrose non-fermenting 1-related protein kinases SAPK8/9/10, which phosphorylate OsRbohB at Ser-140 in ABA signaling. Taken together, these results not only reveal an important regulatory mechanism that directly activates Rboh for ABA-induced H2O2 production but also uncover the importance of this regulatory mechanism in ABA signaling.

The UDP-glucuronic acid decarboxylase OsUXS3 regulates Na+ ion toxicity tolerance under salt stress by interacting with OsCATs in rice.

Overly Na+ ion in soil caused by salt stress has a significant negative impact on the growth and production of crops, especially rice (Oryza sativa L.). Therefore, it is vital for us to clarify how salt stress tolerance in rice is caused by Na+ ion toxicity. The UDP-glucuronic acid decarboxylase (UXS) is a critical enzyme in the biosynthesis of UDP-xylose, which is the key substrate of cytoderm synthesis in plants. In this study, we found that OsUXS3, a rice UXS, is a positive regulator to regulate Na+ ion toxicity under salt stress by interacting with OsCATs (Oryza sativa catalase; OsCAT). The expression of OsUXS3 was significantly up-regulated under NaCl and NaHCO3 treatments of rice seedlings. Meanwhile, by the genetic and biochemical evidence, knockout of OsUXS3 significantly increased reactive oxygen species (ROS) levels and decreased CAT activity under NaCl and NaHCO3 treatments in tissue. Furthermore, knockout of OsUXS3 caused excessive accumulation of Na + ion and rapid loss of K+ ion and disrupts Na+/K+ homeostasis under NaCl and NaHCO3 treatments. Based on the results above, we can conclude that OsUXS3 might regulate CAT activity by interacting with OsCATs, which is not only characterized for the first time but also regulating Na+/K+ homeostasis, positively regulating the Na+ ion toxicity tolerance under salt stress in rice.