Genomic Characterization of SiGRFs in Foxtail Millet and SiGRF1-overexpression in Arabidopsis thaliana Promotes Plant Avoidance of Salt Stress

In plants, 14-3-3 proteins are recognized as mediators of signal transduction and function in both development and stress response. However, their functions have not been reported in the C4 crop foxtail millet. Here, phylogenetic analysis categorized foxtail millet 14-3-3s (SiGRFs) into ten discrete groups (Clusters I to {square}). Transcriptome and qPCR analyses showed that all the SiGRFs responded to at least one abiotic stress. All but one SiGRF-overexpressing (OE) Arabidopsis thaliana line (SiGRF1) exhibited insensitivity to abiotic stresses during seed germination and seedling growth. Compared with the Col-0 wild-type, SiGRF1-OEs had slightly lower germination rates and smaller leaves. However, flowering time of SiGRF1-OEs occurred earlier than that of Col-0 under high-salt stress. Interaction of SiGRF1 with a foxtail millet E3 ubiquitin-protein ligase (SiRNF1/2) indicates that the proteinase system might hydrolyse SiGRF1. Further investigation showed that SiGRF1 localized in the cytoplasm, and its gene was ubiquitously expressed in various tissues throughout various developmental stages. Additionally, flowering-related genes, WRKY71, FLOWERING LOCUS T, LEAFY and FRUITFULL, in SiGRF1-OEs exhibited considerably higher expression levels than those in Col-0 under salinity-stressed conditions. Results suggest that SiGRF1 hastens flowering, thereby providing a means for foxtail millet to complete its life cycle and avoid further salt stress. HighlightSiGRFs in foxtail millet: SiGRF1 hastens flowering in transgenic Arabidopsis thaliana exposed to salt stress