Figure 1. The regulation model of chilling tolerance by OsMAPK3-OsbHLH002-OsTPP1 pathway in rice.
Transcription factor OsbHLH002 can be ubiquitinated by OsHOS1 and degraded by 26S-proteasome. Under chilling condition, cold-activated OsMAPK3 phosphorylates OsbHLH002 and retards OsbHLH002 degradation. Phospho-OsbHLH002 directly activates OsTPP1 transcription, leading to the accumulation of the osmoprotectant trehalose and increase of chilling
Local temperature anomalies caused by global climate change directly threaten crop production. Understanding the mechanisms of cold tolerance is an effective way for molecular breeding of crops. The primary signal transduction pathway of chilling tolerance has been established in rice, however, the regulatory mechanisms among the diverse components are largely unknown. The rice bHLH family of transcription factor has more than 100 members, of which OsbHLH002 has the highest homology with Arabidopsis ICE1 (hence also called OsICE1) and is one of the core members in the cold signaling pathway in rice. Previous study by Chong’s group showed that overexpression of wild rice OrbHLH2 in Arabidopsis enhanced its osmotic stress tolerance (xxx et al., J Plant Physiology, 2009). A recent study by the group discovered that the transactivation activity and accumulation of OsbHLH002 were regulated by protein kinase OsMAPK3 and E3 ubiquitin ligase OsHOS1, resulting in increase of trehalose, an osmotic protectant, which confers rice chilling tolerance.
Under chilling stress, the cold-activated OsMAPK3 phosphorylated OsbHLH002/OsICE1 directly to enhance its transactivation activity. Moreover, OsMAPK3 attenuated the OsbHLH002-OsHOS1 interaction to lead to reduced ubiquitination and degradation of OsbHLH002. The increase of protein content and transactivation activity of OsbHLH002 effectively activate the expression of OsTPP1 (encoding trehalose-6-phosphatase) to promote the hydrolysis of trehalose-6-phosphate, increase trehalose content and enhance rice chilling tolerance. These results established a novel pathway OsMAPK3-OsbHLH002-OsTPP1 which transduces the cold signal from kinase cascade system to nucleus and promotes synthesis of osmotic protectant to regulate the chilling tolerance in rice.
This work has been published in Developmental Cell on December 18th, 2017. The postdoctor Zeyong Zhang is the first author. Prof. Yunyuan Xu and Prof. Kang Chong are the corresponding authors of this article. This research was supported by grants from the Chinese Ministry of Agriculture (2016ZX08009003-002), the Chinese Academy of Sciences (XDA08010205) and the National Natural Science Foundation of China (31400238).
Article link: https://doi.org/10.1016/j.devcel.2017.11.016