The bZIP 73 transcription factor controls rice cold tolerance at the reproductive stage

Abstract

Summary: Cold temperature during the reproductive stage often causes great yield loss of grain crops in subtropical and temperate regions. Previously we showed that the rice transcription factor bZIP 73 Jap plays an important role in cold adaptation at the seedling stage. Here we further demonstrate that bZIP 73 Jap also confers cold stress tolerance at the reproductive stage. bZIP 73Jap was up‐regulated under cold treatment and predominately expressed in panicles at the early binucleate and flowering stages. bZIP 73 Jap forms heterodimers with bZIP 71, and co‐expression of bZIP 73Jap and bZIP 71 transgenic lines significantly increased seed‐setting rate and grain yield under natural cold stress conditions. bZIP 73 Jap:bZIP 71 not only repressed ABA level in anthers, but also enhanced soluble sugar transport from anthers to pollens and improved pollen grain fertility, seed‐setting rate, and grain yield. Interestingly, bZIP 73 Jap:bZIP 71 also regulated the expression of qLTG 3‐1Nip, and qLTG 3‐1Nip overexpression lines greatly improved rice tolerance to cold stress during the reproductive stage. Therefore, our work establishes a framework for rice cold stress tolerance through the bZIP 71‐bZIP 73 Jap‐qLTG 3‐1 Nip‐sugar transport pathway. Together with our previous work, our results provide a powerful tool for improving rice cold stress tolerance at both the seedling and the reproductive stages.