Genome-wide identification and involvement of litchi SPL genes in flowering in response to cold and leaf maturity

摘要

Litchi (Litchi chinensis Sonn.) flowers from shoot apical meristems after exposure to prolonged cold differently depending on maturity. The molecular mechanism defining that interaction of cold with maturity is not fully understood. In the present study, potted litchi plants with terminal flushes at mature and turning stage were treated with 60-days of cold. The mature plants, but not the turning plants, were competent to flower, indicating the importance of terminal flush maturity on litchi flowering. This result could be explained by the difference in accumulation of soluble sugars in the apical leaves on terminal flushes. To explore this link, the miR156/SPL (SQUAMOSA-Promoters Binding Protein-like) module, a dominant sugar-mediated flowering regulator, was investigated. Eighteen SPL homologues were identified, 11 of which were up-regulated during the transition from juvenile to adult. Ten LcSPLs were highly expressed in response to cold, but only LcSPL1 and LcSPL2 correlated with the age-dependent flowering in response to cold. Further, 12 LcSPLs, putative targets of LcmiR156, were subjected to transient co-expression assays in tobacco leaves. LcSPL3 and LcSPL10 showed direct binding to the LcFT1 promoter in vitro and in vivo. This trans-activation was verified by yeast one-hybrid (Y1H) assays.