Functional Analysis Of Two Genes Of Poncirus Trifoliata, PtrMYB And PtrF3E1

Citrus is one of the most important fruit trees in China and most of the citrus cultivars are susceptible to cold. Poncirus trifoliata, the most widely used root stock, is tolerant to low temperature, but sensitive to drought. Therefore, it is of great value for the citrus industry to improve the stress tolerance of both the scion and rootstock. Gene engineering is a powerful approach to enhance stress tolerance of plant, while the key is the cloning and functional identification of resistant genes. PtrMYB transcription factor and PtrF3El (a beta amylase gene) are two stress-related genes previously cloned by our lab. The expression patterns of them under various stresses (dehydration, salt, low temperature, ABA and maltose treatments) were analyzed. In order to identify the functions of these two genes, they were introduced into tobacco by Agrobacterium mediated transformation. The over-expression lines were challenged by different stresses as mentioned above. The main results are as follows:1. Real time RT-PCR analysis suggested that PtrMYB was inducible by dehydration, low temperature, salt and ABA treatments, with different expression patterns. Subcellular localization analysis showed that it was localized in the nuclear.Five over-expression lines were obtained,1#,7#,27#,29#,39#and60#. In the dehydration treatment of27#,39#and the wild type (WT), the over-expression lines showed lower relative water loss and less accumulation of superoxide anion by NBT staining. Under salt treatment, WT showed more severe etiolation and chlorophyll content measurement supported this phenomenon. Polyamines (PAs) play an important role in plant stress resistance. The expressions of ADC, ODC and SPDS (genes involved in PAs synthesis) were elevated in the over-expression lines and positively correlated with that of PtrMYB.2. PtrF3E1could be induced by dehydration, salt, low temperature treatments but maltose treatment suppressed its expression. Transgenic tobacco materials were created and four over-expression lines were obtained (6#,11#,22#and25#). The over-expression lines suffered frow less damage than the WT under low temperature and salt treatment, indicating that this gene could function in the stress resistance.