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Two Xanthomonas Extracellular Polygalacturonases, PghAxc and PghBxc, Are Regulated by Type III Secretion Regulators HrpX and HrpG and Are Required for Virulence

May 2008 , Volume 21 , Number  5
Pages  555 - 563

Lifeng Wang,1,2 Wei Rong,1,2 and Chaozu He1

1State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, Peoples Republic of China; 2Graduate School of Chinese Academy of Sciences, Beijing, 100039, Peoples Republic of China

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Accepted 11 January 2008.

Xanthomonas campestris pv. campestris, the causal agent of black rot disease, produces a suite of extracellular cell-wall degrading enzymes (CWDE) that are involved in bacterial virulence. Polygalacturonase (PG) is an important CWDE and functions to degrade the pectic layers of plant cell walls. Although previous studies have documented the virulence functions of PG in Erwinia and Ralstonia species, the regulation of PG genes still needs to be elucidated. In this study, we identified two novel PG genes (pghAxc and pghBxc) encoding functional PG from X. campestris pv. campestris 8004. The expressions of these two PG genes are regulated by the type III secretion regulators HrpX and HrpG and the global regulator Clp. These PG genes could be efficiently induced in planta and were required for the full virulence of X. campestris pv. campestris to Arabidopsis. In addition, these PG were confirmed to be secreted via the type II secretion system in an Xps-dependent manner.

Additional keywords:hydrolysis, pectin, pathogenesis.

© 2008 The American Phytopathological Society