LcFT1基因启动子决定荔枝成花时间的机制研究

Flowering greatly influence litchi yield and maturation time. Our previous studies had demonstrated that low-temperature induces the expression of LcFT1 in litchi leaves and then leads to flowering. In addition, we found that two types of LcFT1 promoter existed in different litchi cultivars. The LcFT1 promoters in the early-flowering cultivars belonged to one type whereas LcFT1 promoters in the late-flowering cultivars belonged to another one. This promoter difference caused easier and earlier flowering of early-flowering litchi than that of late-flowering litchi. However, the molecular mechanism of this phenomenon is not clear. In this study, we propose to use promoter reconstitution of LcFT1 promoter to identify the key different cis-acting elements or sequences between early- and late-flowering litchi. Then, yeast one-hybrid system will be carried out to identify transcription factors that binding to LcFT1 promoters of early- and late-flowering litchi and then compare difference. Our previous studies also found that two MYB transcription factors were highly related to LcFT1. Hence, the interaction between the two MYB transcription factors and LcFT1 promoter of early- and late-flowering litchi will be verified. Finally, we investigated the functions of the different transcription factors. The expected results from the above research will help further clarify the molecular regulation mechanism underlying the different flowering timing of early- and late-flowering litchi and will provide relevant theoretical guiding for litchi artificial florescence and fruit maturity regulation.

成花是影响荔枝产量和熟期的关键因素，申请者前期研究证明低温能够诱导荔枝叶片中开花基因LcFT1的表达进而导致其成花，还发现荔枝LcFT1基因启动子有两个类型，早花荔枝是一个类型，晚花荔枝是另一个类型，这种差异导致了早花荔枝易成花并早于晚花荔枝。然而LcFT1基因启动子差异导致早、晚花荔枝成花时间不同的机制尚不清楚。本项目拟通过早、晚花荔枝LcFT1基因启动子重组实验明确两者中起关键作用的差异顺式作用元件或碱基序列，进一步采用酵母单杂交等技术筛选作用于早、晚花荔枝LcFT1基因启动子的转录因子，比较两者差异。前期研究还发现2个MYB转录因子与LcFT1基因高度关联，拟采用酵母单杂交等技术直接验证两者与早、晚花荔枝LcFT1基因启动子的互作。最后分析筛选获得的差异转录因子的功能。通过以上研究以期探明LcFT1基因启动子决定荔枝成花时间的分子调控机制，为荔枝的花期人工调控和产期调节提供理论指导。

荔枝是著名的亚热带果树，然而每年不能够稳定成花导致产量没保障是长期以来影响荔枝产业发展的主要难题。前期研究证明低温能够诱导荔枝叶片中开花基因LcFT1的表达进而导致其成花。本项目研究发现荔枝LcFT1基因启动子有两个类型，分别命名为“易成花型”和“难成花型”，进而导致三种基因型荔枝，即：“纯合易成花型”、“纯合难成花型”以及两者的“杂合型”，并且含有“易成花型”启动子的荔枝易成花且早花。进一步通过LcFT1基因两个类型启动子的重组实验明确两者中起关键作用的差异顺式作用元件或碱基序列，采用酵母单杂交等技术筛选作用于早、晚花荔枝LcFT1基因启动子的转录因子并比较两者差异，最后研究差异转录因子的功能。结果表明存在“易成花型”启动子中的ABRE和WRKY等差异顺式作用元件可能是导致两个类型LcFT1基因转录活性差异的一个主要原因，并且筛选获得一个可能起关键作用的bZIP转录因子（命名为LcbZIP1）。基于以上研究，根据LcFT1基因启动子序列的差异，设计了高效精准的分子标记，并将其应用于易成花和难成花荔枝种质资源的鉴定和育种上。以上分子标记能够在幼苗期鉴定易成花和难成花荔枝种质资源，显著缩短了易成花荔枝品种人工杂交育种周期，而且大大节省了人力、物力和土地资源。本研究将有助于进一步阐明荔枝开花时间的分子调控机制，并且为易成花荔枝品种的选育提供理论指导。