Convergent and divergent signaling pathways in C3 rice and C4 foxtail millet crops in response to salt stress

Abstract

Salt stress is a global constraint on agricultural production. Therefore, the development of salt tolerant plants has become a current research hotspot. Salt tolerance evolves more frequently in C grass lineages. However, few studies have been carried out to explore the molecular bases underlying salt stress tolerance in C crop foxtail millet. In this study, we performed a multi-pronged approach spanning the omics analyses of transcriptomes and physiological analysis of C crop rice and C model crop foxtail millet in response to salt stress. Our results revealed specifically compared to C rice, C foxtail millet has upregulated ABA and notably reduced CK biosynthesis and signaling transduction under salt stress. Salt stress in C rice plants triggered rapid downregulation of photosynthesis related genes, which was coupled by severely decreased net photosynthetic rates. In the salt-threatened C rice and C foxtail millet, some stress responsive transcription factors (TFs), such as AP2/ERF, WRKY and MYB underwent strong and distinct transcriptional changes. Based on weighted gene co-expression network analysis (WGCNA), an AP2/ERF transcription factor (.) was identified as a key regulator of salt stress response. To confirmed its function, we generated -knockout lines with CRISPR/Cas9 genome editing in rice and its upstream repressor -overexpressing (-OE) transgenic plants in foxtail millet, which increased salt tolerance. Overall, our study not only provided new insights into the convergent regulation of salt stress responses of foxtail millet and rice, but also shed light on the divergent signaling networks between them in response to salt stress.