Effects Of Over-expression Of GH3.9Gene On The Plant Growth And Development Of Arabidopsis

As a kind of endogenous hormones containing an unsaturated aromatic ring andan acetic acid side chain, auxin is directly involved in many processes such as thegrowth and development of plant roots, the maintainace of apical dominance, theestablishment of embryonic axis, the gravitropism and phototropism of plants, as wellas stimulating the growth of floral organs. Generally, the auxin plays an important rolein adjusting the course of the whole life cycle of plant. The auxin response genes aregenes whose transcription can be quickly activated after the auxin treatment. The GH3gene family, which contains a total of20members in the Arabidopsis, is categorizedin typical primary auxin-responsive genes, It was found that the GH3proteins have asimilar function to auxin (like the indole acetic acid) amino acid synthesis enzymes.The GH3proteins are able to adjust the concentration of active auxin and affect thegrowth and development of plants. They participate in the plant defense responses,thus can enhance the plant resistance. Simultaneously, they are involved in thephotoreaction regulation processes and promote the absorption of light energy.As a special member of the GH3gene family, GH3.9gene appears insensitive tothe low concentration of auxins. While the present study is limited to the GH3.9loss-of-function mutations, this paper aims to investigate the function of itsovere-xpresstion mutants.First, some bioinformatical methods were adopted to predict the gene express andfunction of GH3.9. Combining with the RT-PCR result, we found that the GH3.9geneexpression in wild-type Arabidopsis showed tissues and organs specificity. And theexpression levels of seed, stem, root, leaf and flower decreased orderly.In the second part, the agrobacterium-mediated pEGAD-GH3.9transfection andBastar selection were applied to obtain the homozygous of over-expression mutant.The wild-type and mutant seeds showed similar germination rates. which indicatesthat the GH3.9gene does not regulate the seeds germination. After treating the sowedwild-type and mutant seeds with blue, red and infrared light at various intensity, wefound that the growth of hypocotyls remained unchanged under the darkness and weaklight, while the mutants were more sensitive to the strong light suppression comparingwith wild-type. These results indicated that GH3.9was tightly associated with thelight reaction control mechanism of plant growth. Moreover, the hypocotyls of mutants appeared to grow slower when treated different forms of white light. Then,morphology investigations for wild type and mutants demonstrate that the lengthratios between the stamens and pistil of mutants are obviously lower. The mutantsplant sizes and pod sizes also appeared smaller, but their maturity of plants wassignificantly longer. In summary, it can be concluded that GH3.9gene might play animportant role in the growth and development of plants except the procedure of seedgermination.