MicroRNAs balance growth and salt stress responses in sweet sorghum.

Salt stress is one of the major causes of reduced crop production limiting agricultural development globally. Plants have evolved with complex systems to maintain the balance between growth and stress responses, where signaling pathways such as hormones play key roles. Recent studies revealed that hormones were modulated by microRNAs (miRNAs). Previously, two sweet sorghum inbred lines with different salt tolerance were identified: the salt-tolerant M-81E and the salt-sensitive Roma. The levels of M-81E and Roma endogenous hormones varied differently under salt stress, showing a different balance between growth and stress responses. The miRNA and degradome sequencing showed that many upstream signal transduction transcription factors and hormone-responsive genes were directly induced by differentially expressed miRNA, which were much different between the two sweet sorghum lines. Furthermore, the effect of representative miRNAs on the salt tolerance of sorghum was verified through the transformation system mediated by Agrobacterium rhizogenes. Also, miR-6225-5p inhibited the level of Ca 2+ in the miR-6225-5p overexpressing line by inhibiting the expression of the Ca 2+ uptake gene SbGLR3.1 in the root epidermis, and affected the salt tolerance of sorghum. This study provided evidence for miRNA-mediated growth and stress responses in sweet sorghum.