An endopolygalacturonese gene of Diaporthe helianthi

In the attempt of defining virulence determinants of Diaporthe helianthi, the causative agent of sunflower stem canker, the gene named Dhpg, coding for an endopolygalacturonase, was investigated in the highly virulent strain 8/96 isolated from a diseased plant in France. The 1624 bp coding sequence, in addition to 1343 bp from the upstream region, were cloned, sequenced and analyzed. Dhpg was most closely related to polygalacturonase genes from phytopathogenic fungi, such as Ophiostoma ulmi, O. novo-ulmi, and Gibberella zeae. A Southern blot RFLP analysis proved that Dhpg was represented in single-copy in the genome of the isolate 8/96. Analyses carried out both in vitro on liquid cultures and in vivo on host infected tissues provided evidence of the constitutive expression of the Dhpg transcript under all tested conditions. Moreover, an European collection of D. helianthi isolates was screened for the presence of Dhpg homologues by PCR, revealing the same single band in all French and Yugoslavian isolates, while one Romanian and all Italian isolates displayed a variable pattern. This genetic variability related to the different D. helianthi geographic origin is consistent with data previously reported for different loci on the same set of isolates. This is the first report concerning a polygalacturonase gene in D. helianthi.