| The ability to acquire nutrients from the host is essential for a pathogen to cause disease. Among those nutrients, carbon nutrient is one of the most important elements. Like other organisms, pathogens may use gluconeogenesis to synthesize glucose from non-sugar compounds when there is not sufficient hexose in their niche. The importance of the gluconeogenesis in Xcc virulence have been demonstrated recently in our laboratory. Glucose-6-phosphate isomerase (PGI) is another key enzyme in gluconueogenesis. According to Xcc 8004 genome annotation, Glucose-6-phosphate isomerase was encoded by pgi gene (ORF XC2379 ). To determined the role of this gene in gluconeogenesis and in pathogenesis of Xcc, mutants of pgi gene were constructed by homology plasmid integration method. The carbon utilization ability of the resulting mutant was tested, results showed that the pgi mutant grow poorly in non-carbon MMX medium with acetate, citrate, lactose, pyruvate, succinate, fumarate, or malate as sole carbon source. This indicated that pgi gene is involved in gluconueogenesis. The virulence of pgimutant was tested on Chinses radish (Raphanus sativus L. var. radical us Pers.) by leaf clipping, ten days post-inoculation, lesion length with a mean of 9.9 mm was observed on leaves inoculated with the wild type strain, while mean lesion lengths of 3.6 mm were observed with pgi mutant. This result demonstrated that pgi gene is required for full virulence of Xcc. These results combined with the previously findings in our laboratory that ppsA and maeB, genes encoding key enzymes in gluconeogenesis, are required for Xcc virulence, strongly indicated that the gluconeogenic pathway is important for Xcc virulence.
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