| The growth of Arabidopsis thaliana, which is a kind of typical glycophyte, is seriously restrained in salty environment and it becomes an unattainable goal to finish its growth cycle. However, as the close relative of Arabidopsis thaliana, Thellungiella halophila can resist the assault of high concentration salt and finish its life cycle. Comparison shows that, they have high similarity on the cDNA level, with more than 90% similarity. And more than that the external features of the two also show great common with each other, while there is difference in the two, especially as to the life span, T. halophila leads a much longer life cycle than A.thaliana, which reminds us a possible mechanism of salt tolerance. As we know from ordinary life, the same wheat grown in different temperatures show different salt tolerance ability, so as a possibility it may be true that the growth rate of plant does something with its tolerance to environment stress,for example salt. So we presume that the variation of their ability of salt tolerance may arise from their different life span.To testify our assumption, we should make the T.halophila grow quicker or slower, and measure their ability of salt tolerance, in which way to make correlation between growth rate and salt tolerance. Luckily we get to know the DELLA proteins, which are a series of proteins whose amino acid sequence possesses a conserved domain featured by DELLA, five sequential amino acids, and that is where they get their name. Oryza sativa has only one kind of DELLA protein, while A.thaliana, which has a smaller genome possess five kind of DELLA proteins, they are GAI, RGA, RGL1, RGL2, RGL3, they have different and redundancy functions. The DELLA proteins are the superstar of the recent research, and up to now we get to know that those proteins are transcription factors and play vital roles in the gibberellin signal transduction, that is suppressing the growth of plant. Two papers published in 2008 indicated that DELLA proteins, mainly RGA and GAI can inhibit cell division and elongation. Gibberellin absorbed by cells combine with receptors in the nucleus and integrate with DELLA proteins, then lead them to be degraded by proteasomes, thus release the inhibition of DELLA proteins, and promote the elongation of the stem of plants. If the coding gene of DELLA protein mutated, and lose function, then the plant may grow much faster than normal and become long and slim phenotype, like those plants ich are treated with large amount of gibberellin, while in another condition, the mutation of the DELLA domain of the protein may makes it unrecognized by the receptor and can not be degraded by the proteasome, thus leads to higher concentration of DELLA protein than usual and much more dense inhibition to the grow of plant, at last, lead to the final short stem phenotype, similar to those with gibberellin synthesis gene mutated plant.Then we plan to change the growth rate of T.halophila through changing its amount of DELLA proteins, we can make this by operating the coding gene of the DELLA proteins, then we measure the ability of salt tolerance to correlate the relationship between them. So the first step is to design a pair of degenerate primers, in order to clone the coding gene. Because T. halophila is highly close related with A.thaliana, so we can control the degenerate rate under twenty easily. And following the same route we amplify the sequence of the gibberellin receptor coding gene ThGID1A. We assume that there are no less than five DELLA proteins coding genes in the T.halophila genome, and their functions may be redundancy. So it is impossible to change the grow rate of T.halophila obviously through silencing the ThGAI. We overexpress the ThGAI. to make plant grow slower and overexpress the ThGID1A to make plant grow faster. Then we measure the ability of salt tolerance and make comparison with wild type, thus to correlate the relationship between the growth rate of plant and the ability of salt tolerance.
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