Colonization by the arbuscular mycorrhizal fungus Glomus versiforme induces a defense response against the root-knot nematode Meloidogyne incognita in the grapevine (Vitis amurensis Rupr.), which includes transcriptional activation of the class III chitinase gene VCH3.

Inoculation of the grapevine (Vitis amurensis Rupr.) with the arbuscular mycorrhizal (AM) fungus Glomus versiforme significantly increased resistance against the root-knot nematode (RKN) Meloidogyne incognita. Studies using relative quantitative reverse transcription-PCR (RQRT-PCR) analysis of grapevine root inoculation with the AM fungus revealed an up-regulation of VCH3 transcripts. This increase was greater than that observed following infection with RKN. However, inoculation of the mycorrhizal grapevine roots with RKN was able to enhance VCH3 transcript expression further. Moreover, the increase in VCH3 transcripts appeared to result in a higher level of resistance against subsequent RKN infection. Constitutive expression of VCH3 cDNA in transgenic tobacco under the control of the cauliflower mosaic virus 35S promoter also conferred resistance against RKN, but had no significant effect on the growth of the AM fungus. We analyzed beta-glucuronidase (GUS) activity directed by a 1,216 bp VCH3 promoter in transgenic tobacco following inoculation with both the AM fungus and RKN. GUS activity was negligible in the root tissues before inoculation, and was more effectively induced after inoculation with the AM fungus than with RKN. Moreover, GUS staining in the mycorrhizal transgenic tobacco roots was enhanced by subsequent RKN infection, and was found ubiquitously throughout the whole root tissue. Together, these results suggest that AM fungus induced a defense response against RKN in the mycorrhizal grapevine roots, which appeared to involve transcriptional control of VCH3 expression throughout the whole root tissue.