Studies On The Regulation Mechanism Of Pathogenesis For Four IAA Synthesis -related Genes In Xanthomonas Oryzae Pv.Oryzae

As one of the most important diseases on rice, bacterial blight ?BB?, caused by Xanthomonas oryzae pv. oryzae ?Xoo?, lead to great loss of rice yield and quality in China and some areas of Southeast Asia. In nature, plant relies on its relatively complete defense system to resist the invasion of pathogenic bacteria. However pathogenic bacteria produces a variety of virulence factors in order to break through the defense system and obtain nutrients and more living space.Plant hormone, trace organic substances synthesized in plants, plays an important role in the division, growth, differentiation, dormancy and fading of plant cells. The study found that many plant pathogens can synthesize the similar compounds of plant hormone, which can be used to regulate and disrupt the normal growth and metabolism of the host plant, resulting in many morphological lesions, as stunting, excessive growth and malformations of plant.In this study, we focused on the four PXO99A mutants and its complementary strains previously generated as IAA deficiency, in which genes predicted to encode protein involves in IAA synthesis. These included the four mutants, P?pxo₀4004, P?pxo₀4823, P? pxo₀0867 and P?pxo₀3584, as well as their complementary strains CP?pxo₀4004, CP ?pxo₀4823, CP?pxo₀0867 and CP?pxo₀3584 respectively. Firstly, we validated the results that the IAA contents were declined in all four mutated strains. Then we expressed the two proteins, pxo₀4823 and pxo₀0867, by using prokaryotic expression system. Unfortunately, we have not identified any nitrilase activity with either pxo₀4823 or pxo₀0867 in vitro. Furthermore, compared with wild strain PXO99A, all four mutated strains were significantly increased virulence to rice. To explore the possible mechanism for the enhanced virulence in IAA synthesis-related gene mutations, we have investigated the profile of secretion proteins after induced with XOM medium treatment. The results showed that the species and amount of secretion proteins were more in mutations than in PXO99A strain. The differentially secreted proteins were characterized by two-dimensional electrophoresis technology and mass spectum analysis, and we have identified four Xoo-secreted proteins which involved in plant cell degradation, drug-resistance and flagellum development. These results were indicated that the IAA synthesis-related genes were regulated the pathogenicity by controlling the synthesis or secretion of the virulence secreted proteins in Xoo.