Short vegetative phase (SVP), a MADS-domain transcription factor, was shown to act as a repressor of flowering in arabidopsis (Arabidopsis thaliana). Although the role of SVPs in flowering is well characterized in the model plant arabidopsis, little is known in evergreen woody litchi (Litchi chinensis). In this study, three litchi SVP homologs (LcSVP1, LcSVP2, and LcSVP3) were cloned, and the bioinformatic analysis of the LcSVPs was carried out to identify their molecular characteristics. Their expression patterns in the apical meristem (AM) during the transition from vegetative to reproductive phase were studied under natural flowering inductive conditions. Also, brassinosteroid (BR) treatment under low temperature conditions was performed to elucidate the role of LcSVPs in the BR-regulated flowering. The results showed that LcSVPs belonged to the MADS superfamily. LcSVP relative expression levels in AMs of the early- and late-flowering cultivars showed decreasing trends with the transition from vegetative to reproductive growth. Under low temperature condition, relative expression levels of LcSVP1, LcSVP2, and LcSVP3 in AMs or panicle primordia showed decreasing trends, whereas those in the AMs of the BR-treated trees remained at relatively high levels. Relative expression analysis of the litchi homolog, flowering locus t 1 (LcFT1), showed that the BR-treated leaves had lower relative expression level than nontreated control leaves. The findings suggest that LcSVPs act as repressors involved in flowering in natural conditions and the BR-regulated flowering.
Jiaqi Hu, Hye-Ji Kim, Houbin Chen and Biyan Zhou
Hai-Fang Yang, Hye-Ji Kim, Hou-Bin Chen, Jillur Rahman, Xing-Yu Lu and Bi-Yan Zhou
Litchi trees flower at the apex of terminal shoots. Flowering is affected by the maturity of terminal shoots before growth cessation occurs during the winter. In this study, we focused on changes of flowering in three important cultivars, Guiwei, Feizixiao, and Huaizhi, from Dec. 2012 to Mar. 2013 under natural winter conditions. Flowering rate, carbohydrate accumulation, and expression of the flowering-related genes were determined at three different developmental stages of terminal shoots with dark green, yellowish green and yellowish red leaves, respectively. The results showed that the total soluble sugar and starch contents in the dark green leaves were the highest, whereas those in the yellowish red leaves were the lowest. Trees with dark green terminal shoots had the highest flowering rates, whereas those with yellowish green or yellowish red shoots had relatively lower flowering rates. SPAD was highest in dark green leaves and lowest in yellowish red leaves at the start of the trial. The SPAD value of yellowish red leaves slightly increased but did not reach the levels of the dark green leaves, whereas levels of the other leaf stages remained fairly constant. Expression level of the litchi homolog FLOWERING LOCUS C (LcFLC), the floral inhibitor in yellowish red leaves, increased from 16 Jan., whereas that in dark green leaves declined to a level lower than the yellowish red leaves on 4 Feb. Expression level of the litchi homolog CONSTANTS (LcCO), the floral promoter in dark green leaves, was higher than that of yellowish red leaves before 26 Jan. Expression level of the litchi homolog FLOWERING LOCUS T 2 (LcFT2), encoding florigen, was higher in dark green leaves than in the other two leaf types. Our results suggest that terminal shoots should be matured and leaves should turn green for successful flowering. Mature leaves had higher expression levels of the floral promoter and florigen. In litchi production, leaves of the terminal shoots (potential flowering branches) should be dark green during floral induction and differentiation stages, and winter flushes should be removed or killed.