Comparison of endo‐polygalacturonase activities of citrus and non‐citrus races of Geotrichum candidum, and cloning and expression of the corresponding genes

Abstract

summary Geotrichum candidum citrus race, a fungus that causes a sour rot disease in citrus fruits, secretes an endo-polygalacturonase (PG) that may facilitate the disease. There also exists a non-citrus race that is non-pathogenic to citrus fruits. In this research, we found that the PG activity of the citrus race isolates was much higher than that of the non-citrus race isolates in culture medium and inoculated lemon peel, and that there was a significant correlation between the PG activity and pathogenicity. We isolated the two corresponding PG genes, S31pg1 and S63pg1, from citrus race S31 and non-citrus race S63, respectively. S31PG1 and S63PG1 consisted of 368 and 369 amino acids, respectively. The two PG genes showed 68% identity at the amino acid level. In expression studies, S31pg1 transcript was detected in mycelia grown in liquid cultures of citrus race S31 containing either glucose, pectin or lemon peel broth. The transcript was also detected in lemon peel inoculated with the isolate. On the other hand, no transcript of S63pg1 was detected in mycelia grown on any liquid cultures of non-citrus race S63 and lemon peel inoculated with the isolate. These results indicate that PG may play an important role in the development of the sour rot symptom and be involved in the difference of pathogenicity between the two races.

How Way Leads on to Way

“…Results suggested that the higher initial amount of enzyme produced in vivo by the citrus race and the higher sensitivity of the pectin in situ to this enzyme were the two main factors governing the unique virulence of the citrus race on citrus fruits (51). A later manuscript by Nakamura et al (73) showed 68% identity at the amino acid level between endo-PG from citrus and noncitrus races, suggesting that the two enzymes are similar but not identical. It could be hypothesized that the endo-PG of the citrus race can efficiently degrade the protopectin in citrus fruits (water-insoluble pectic sustenance present in intact tissue), whereas the noncitrus race cannot.…”

Establishment of heterologous expression of polygalacturonase S63PG1 from nonpathogenic isolate S63 of Geotrichum candidum

“…Previously, we isolated three PG genes from G. candidum, S31pg1 (AB099408) and S31pg2 (AB0994089) from pathogenic isolate S3 and S63pg1 (AB062511) from nonpathogenic isolate S63 (Nakamura et al 2001(Nakamura et al , 2003. Using PGs expressed by a yeast expression system, we clarified that S31PG1 was important in pathogenicity in lemon fruit, but S31PG2 was not (Nakamura et al 2003).…”

Polygalacturonase S31PG1 from Geotrichum candidum citrus race S31 expressed in Schizosaccharomyces pombe versus S31PG2 regarding soft rot on lemon fruit

“…We previously isolated a PG gene, S31pg1, cDNA from G. candidum citrus race S31 (Nakamura et al 2001). S31pg1 was expressed in both cultures and lemon fruit infected with the citrus race S31: The gene was not catabolite-repressed (Nakamura et al 2001).…”