The B-box transcription factor BnBBX22.A07 enhances salt stress tolerance by indirectly activating BnWRKY33.C03.

ABSTRACT

Salt stress has a detrimental impact on both plant growth and global crop yields. B-box proteins have emerged as pivotal players in plant growth and development regulation. Although the precise role of B-box proteins orchestrating salt stress responses in B. napus (Brassica napus) is not well understood in the current literature, further research and molecular explorations are required. Here, we isolated the B-box protein BnBBX22.A07 from B. napus. The overexpression of BnBBX22.A07 significantly improved the salt tolerance of Arabidopsis (Arabidopsis thaliana) and B. napus. Transcriptomic and histological analysis showed that BnBBX22.A07 enhanced the salt tolerance of B. napus by activating the expression of reactive oxygen species (ROS) scavenging-related genes and decreasing salt-induced superoxide anions and hydrogen peroxide. Moreover, BnBBX22.A07 interacted with BnHY5.C09, which specifically bound to and activated the promoter of BnWRKY33.C03. The presence of BnBBX22.A07 enhanced the activation of BnHY5.C09 on BnWRKY33.C03. Overexpression of BnHY5.C09 and BnWRKY33.C03 improved the salt tolerance of Arabidopsis. Functional analyses revealed that BnBBX22.A07-mediated salt tolerance was partly dependent on WRKY33. Taken together, we demonstrate that BnBBX22.A07 functions positively in salt responses not only by activating ROS scavenging-related genes but also by indirectly activating BnWRKY33.C03. Notably, our study offers a promising avenue for the identification of candidate genes that could be harnessed in breeding endeavours to develop salt-resistant transgenic crops.