Abstract
Floral induction in litchi is influenced by multiple environment cues including temperature and soil water condition. In the present study, we determined that a combined treatment consisting of 14-day drought imposed prior to exposure to 35-day low temperature (T3) significantly promoted litchi flowering relative to the low temperature alone (T2), suggesting an integrative effect of drought and low temperature on litchi floral initiation. Analysis of transcriptomic changes in leaves from different treatments showed that 2,198 and 4,407 unigenes were differentially expressed in response to drought and low temperature, respectively. 1,227 of these unigenes were expressed in response to both treatments, implying an interaction of drought and low temperature on expression of genes involved in litchi floral initiation. Additionally, 932 unigenes were consistently differentially expressed during floral induction between T2 and T3 plants, which potentially accounts for the difference of flowering time. Thirty-eight transcription factors out of these 932 unigenes were identified as hub genes with central roles in regulation of litchi floral induction. The expression of litchi homologs of well-known flowering genes was also investigated, and one Flowering Locus T (FT) homolog may play a crucial role in litchi flowering in responses to drought and low temperature.
Highlights
Which represses expression of another important flowering promoter SUPPRESSOR OF OVEREXPRESSION OF CO1 (SOC1)[14,15,16,17]
There were no flowers in T1 plants, and T5 plants rarely flowered, suggesting that low temperature is required for litchi floral initiation
Plant flowering time is determined by endogenous signals and environmental cues, including phytohormones, photoperiod, vernalization process, and phase transition from juvenile to adult[9,25,26]
Summary
Which represses expression of another important flowering promoter SUPPRESSOR OF OVEREXPRESSION OF CO1 (SOC1)[14,15,16,17]. Previous studies have shown that day length-dependent genes including CO can play complementary and important roles in temperature signaling in floral initiation[21,22]. The integrative effect of drought and temperature on plant flowering-genes has yet to be further studied. Drought treatment, low temperature treatment, and drought followed low temperature treatment were imposed on potted litchi plants to investigate the effects of water stress and low temperature on floral initiation. The expression profiles of unigenes from different treatments were multiply compared and characterized to identify potentially important genes involved in litchi floral initiation in responses to drought and cold. The hub genes that potentially play central regulative roles in litchi floral induction were isolated. The results provide evidence for regulation of litchi floral induction, and establish a foundation for advanced research on functional flowering-genes in litchi or similar plants
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