| Bacterial blight, caused by Pseudomonas syringae pv. glycinea, is the most common bacterial disease of soybean. It was identified in Nebraska as early as 1906, then it was found occurred wherever soybeans were grown and have emerged a serious problem in main production area. Recent years, a disease with symptoms similar to bacterial spots was initially observed on soybean in the northeastern of China, one of the major soybean production areas. After extensive field investigation,25 samples of diseased soybean leaves were collected in the northeast of China, mainly in Jiamusi of Heilongjiang Province and Changchun of Jilin Province, and bacterial blights were isolated and purified. By satisfying Koch's postulates, it was established that these strains caused the disease.Six isolates from different geographic locations and different soybean species were selected for detailed morphological and molecular studies. All isolates were grouped by 16S rDNA into the Pseudomonas genus. Then, avrD gene analysis suggested that all isolates had high homology to Pseudomonas syringae pv.glycinea. Interestingly, fatty acid methyl esters (FAME) analysis revealed that 4 isolates were highly similar to the typical Pseudomonas. syringae pv. glycinea, but 2 isolates, which were highly similar to Pseudomonas. syringae, could not be identified to the pathovar. On the basis of the results of all studies, we concluded that the disease found on soybeans from Jiamusi of Heilongjiang Province and Changchun of Jilin Province was bacterial spots, which was caused by Pseudomonas. syringae pv. glycinea.Phytopathogenic bacteria suppress plant innate immunity and promote pathogenesis by injecting proteins called typeⅢeffectors into plant cells using a typeⅢprotein secretion system. These typeⅢeffectors use at least three major strategies to alter host responses. One strategy is to alter host protein turnover, either by direct cleavage or by modulating ubiquitination and targeting to the 26S proteasome. Another strategy involves alteration of RNA metabolism by transcriptional activation or ADP-ribosylation of RNA-binding proteins. A third major strategy is to inhibit the kinases involved in plant defence signalling, either by removing phosphates or by direct inhibition.To study the pathogenesis of the soybean pathogen Pseudomonas syringae pv. glycinea, 2 typeⅢ-secreted effectors were cloned by inverse PCR (iPCR). The full length of HopAB1 gene contained a 1587 bp open reading frame, encoding 523 amino acid residues; The full length of HopAF1sgene contained a 855 bp open reading frame, encoding 284 amino acid residues. The two genes registered in GenBank with accession numbers JF826562 and JF826563. The nucleotide sequence of HopAB1 and HopAFl gene showed 69%～96% and 86%～99% of homology respectively compared with those of different reference strains published in GenBank by sequence analysis. The two effectors have no signal peptide. The secondary stucture of the two proteins were composed of random coil, alpha helix and extend strand. The N terminus of HopAB 1 is sufficient for E3 ubiquitin ligases activites. Furthermore, the HopAB 1 tertiary structure was build based on A chain of 2FD4. The two effectors were inserted into the binary PVX vector, transformed into Agrobactrium tumefaciens GV3101, and the Agrobacterium-mediated transient expression experiments confirmed that two effectors functioned to inhibit the ability of the pro-apoptotic protein Bax inducing PCD in plant. Furthermore, infection experiment results showed that the effectors can promote ability of Phylophthora nicotianae infecting tobacco (Nicotiana benthamiana). Two cloned genes both belong to suppressive effector, our research is lay a foundation for revealed the molecular pathogenesis of Pseudomonas syringae pv. glycinea. |
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