GRAS transcription factors mediate flowering through signaling pathways of gibberellin and circadian rhythm in Lonicera japonica Thunb.

Abstract

BackgroundLonicera japonica Thunb. (Caprifoliaceae) flower has been a traditional herbal medicine in both China and Japan and the regulatory role of transcription factors (TFs) during flowering of L. japonica has attracted the attention of researchers. However, GRAS family TFs have not been identified in L. japonica, and their regulatory role in the floral development of L. japonica has not been revealed. MethodsWe selected flowers of L. japonica at five growth stages (S1. young alabastrum, S2. green alabastrum, S3. whole white alabastrum, S4. silvery flower, and S5. golden flower) for a comprehensive GRAS TF analysis, and determined the expression levels of GA biosynthesis and signaling pathway and plant circadian rhythm signaling pathway related genes. The content change of GA1 and GA4 in the flowers of L. japonica at five floral growth stages was determined by LC-MS/MS. ResultsWe explored the function of LjGRAS TFs in the context of a protein-protein interaction (PPI) network. The proteins that interacted with LjGRAS proteins belonged to two pathways: GA biosynthesis and signaling pathway and plant circadian rhythm signaling pathway. The expression of GAI (LjGRAS14); GA20OX; GA3OX; RGA1 (LjGRAS15; 33); RGL3 (LjGRAS17); GAMYB; PIF3; ELF3; FT and CO showed a trend of first high in S1-S3 and then low in S4-S5, while the expression of GID1; GA2OX; CRY2; LHY; SOC1; GI and FKF1 was just the opposite. The concentration of GA1 and GA4 is the highest in S1 and decreases significantly in S2, S3, S4 and S5. In the early stage of flower development (S1-S3), the high level of GA1 and GA4 content is attributed to the high expression levels of GA20OX and GA3OX, while in the late stage of flower development (S4-S5), the decrease of GA1 and GA4 content leads to the accumulation of DELLA proteins, which changes the expression of genes related to plant circadian rhythm signaling pathway. ConclusionAn orderly change in expression of genes related to GA biosynthesis and signaling pathway and plant circadian rhythm signaling pathway in the transition from vegetative growth to reproductive growth of L. japonica was observed, which provided an insight into the molecular mechanism and transcriptional regulation of L. japonica flower from bud to maturity.