Regulation Of Brassinosteroids On Flowering Of Litchi And Its Relationship With LcSVP

Litchi?Litchi chinensis Sonn.?is Sapindaceae.It is a tropical and subtropical evergreen tree with colored,delicious,and nutritious fruit.Low temperature is required for floral differentiation.However,the frequently occured mild winter or extremely low temperature often affect floral differentiation of the high quality late-flowering litchi.Brassinosteroids regulate many important growth and development processes.Exogenous Brassinolide can accelerate the growth and development of wild-type Arabidopsis thaliana,resulting in early.It also enhances chilling tolerance.SVP is the key gene for temperature regulation and flowering,and plays an important role in the dormancy of fruit trees.While BR interact with SVP through BZR1.SVP was a connection point between BR and flowering time regulation network.In this study,we investigated the effects of exogenous brassinolide on the flower bud differentiation under inductive low temperature and extremely low temperature conditions,explored the expression pattern of LcSVPs gene,and studied the function of gene by TRV-based transient expression system.The results are as follows:?1?Under the inductive low temperature condition,late-flowering'Huaizhi'litchi trees were treated with 18/13?for 45 d and were sprayed with 24-EBR or distilled water,respectively.The results showed that,flowering related physiological indexes of the 24-EBR treated trees were significantly lower than control.The relative expression of LcFT1 increased sharply,while the expression of LcFT1 was almost undetectable in 24-EBR and high temperature treated trees,suggesting that 24-EBR inhibited the flower bud differentiation of'Huaizhi'under the low temperature condition.?2?Distilled water as control,GA₃ in the concentration of 208?M,and 24-EBR in the concentration of 0.5?M,1?M,2?M were sprayed to potted'Guiwei'trees in open fields.The trees were experienced extremely low temperature on January 24,2016.Red spots were found in the"whitish millets".and leaves were damaged by the low temperature.C hilling injury in GA₃ treated trees were serious,and at last,the trees died.24-EBR significantly reduced the relative conductivity and increased the activity of SOD and POD.It is suggested that exogenous brassinolide can improve the chilling resistance of'Guiwei'litchi.?3?We cloned the full length of LcSVP1,LcSVP2 and LcSVP3.The results of NCBI blastP showed that they belong to MADS superfamily.q RT-PCR analysis showed that LcSVPs genes accumulate mainly in vegetative tissues,especially in buds.The relative expression of LcSVPs gene was significantly decreased before the"whitish millets"stage.The relative expression of LcSVPs gene in the SAMs of controls was significantly lower than that in the 24-EBR treated ones.LcSVPs showed negative relationship with floral formation in litchi.?4?LcSVP1 and LcSVP3 were selected as the target genes,and the expression of LcSVP1 and LcSVP3 were determined in the TRV-based transient expression leaves.The relative expression of LcSVP1 and LcSVP3 was analyzed by multivariate analysis of variance.The results showed that transient expression treatment,24-EBR and the time of virus infection have a significant effect on the relative expressio n of LcSVP1and LcSVP3.And over-expression of LcSVP1,24-EBR spraying and virus infection time are interacted,As to LcSVP3,no interactions were found among the three factors.