Physiological, biochemical, and microscopic analyses of weakened walls of conidia in Colletotrichum graminicola with a disrupted class V chitin synthase gene, chsA

Colletotrichum graminicola (teleomorph, Glomerella graminicola) mutant T30 has a disruption in chsA, which is a class V or a class VI chitin synthase (class VI if recognized). The mutant conidia were significantly easier to fracture with glass beads than conidia of the wild type and two T30-derived strains that were complemented with chsA. Similarly, after extraction in alkali, the walls of significantly more mutant conidia collapsed in comparison to the wild type and the two chsA-complemented strains. These data provide genetic evidence that the chitin synthesized by ChsA is critical for conidial wall strength and rigidity. The conidial wall compositions of the wild type and the T30 strains were compared. The chsA-disrupted conidia had a significantly lower percentage of chitin and an alkaliand trifluoroacetic acid (TFA)insoluble glucan (30 and 15% less, respectively). The mutant had a correspondingly higher content of a TFA-hydrolyzable glucan than the wild type. Both strains had similar percentages of covalently bound protein and alkali-insoluble polysaccharide(s) containing TFAhydrolyzable mannose, galactose, arabinose, xylose, and rhamnose. The significant reduction in both chitin and the TFA-insoluble glucan supports the hypothesis that chitin is present in walls as a chitin-glucan complex and that the glucan’s insolubility is due to its linkage to chitin. q 2003 Elsevier Ltd. All rights reserved.