VdSNF1, the Sucrose Nonfermenting Protein Kinase Gene ofVerticillium dahliae, Is Required for Virulence and Expression of Genes Involved in Cell-Wall Degradation

Abstract

Verticillium dahliae is a soilborne fungus causing vascular wilt in a diverse array of plant species. Its virulence has been attributed, among other factors, to the activity of hydrolytic cell wall-degrading enzymes (CWDE). The sucrose nonfermenting 1 gene (VdSNF1), which regulates catabolic repression, was disrupted in V. dahliae tomato race 1. Expression of CWDE in the resulting mutants was not induced in inductive medium and in simulated xylem fluid medium. Growth of the mutants was significantly reduced when grown with pectin or galactose as a carbon source whereas, with glucose, sucrose, and xylose, they grew similarly to wild-type and ectopic transformants. The mutants were severely impaired in virulence on tomato and eggplant (final disease severity reduced by an average of 87%). Microscopic observation of the infection behavior of a green fluorescent protein (gfp)-labeled VdSNF1 mutant (70ΔSF-gfp1) showed that it was defective in initial colonization of roots. Cross sections of tomato stem at the cotyledonary level showed that 70ΔSF-gfp1 colonized xylem vessels considerably less than the wild-type strain. The wild-type strain heavily colonized xylem vessels and adjacent parenchyma cells. Quantification of fungal biomass in plant tissues further confirmed reduced colonization of roots, stems, and cotyledons by 70ΔSF-gfp1 relative to that by the wild-type strain.

Proteomics-based analysis reveals that Verticillium dahliae toxin induces cell death by modifying the synthesis of host proteins

“…Culture supernatant of V. dahliae induces cotton cell death Phytotoxins or effectors secreted by V. dahliae have been considered to be important in pathogenesis by Verticillium (Tzima et al 2011). When cotton cotyledons were treated with the culture supernatant of V. dahliae, whole V. dahliae culture (including supernatant and conidia, as positive control) and PDB (as negative control), respectively.…”

“…After penetrating the cortex of the root, the fungus passes through the endodermis, invades the xylem vessels, eventually reaching the aerial parts of the plant (Tzima et al 2011). Typical disease symptoms may comprise wilting, stunting, leaf necrosis, vascular plugging and brown vascular discoloration (Fradin and Thomma 2006).…”

“…The occlusion can be due to a physical blockage of the xylem by the pathogen or due to host defense responses that result in vessel plugging (Fradin and Thomma 2006). In recent years, some genes related to V. dahliae pathogenicity have been identified, such as a mitogen-activated protein kinase (VMK1) (Rauyaree et al 2005), a cAMP-dependent protein kinase A (VdPKAC1) (Tzima et al 2010), a glutamic acid-rich protein (VdGARP1) (Gao et al 2010) and a sucrose nonfermenting 1 gene (VdSNF1) (Tzima et al 2011). Proteins that can induce plant cell death have also been isolated from a culture supernatant of V. dahliae such as VdNEP (Wang et al 2004); however, there is still doubt whether any of these play key role in V. dahliae pathogenicity (Zhou et al 2012).…”

Selection of tomato accessions resistant to Verticilium wilt1

“…The PX-116 and PX-123 accessions displayed isolate-specific responses ranging from resistant, when inoculated with the Vet-668 isolate, to susceptible, when inoculated with Vet-157. The possibility of such phenotypic instability may be attributed, in terms of the pathogen, to the existence of a cryptic pathogenic variability within isolates of the same physiological race and an allelic variation and/or different levels of expression of the Ve gene in the host plant (O' Garro & Clarkson 1988, Cherrab et al 2000, Tzima et al 2011.…”

Isolation and functional analysis of the pathogenicity-related gene VdPR3 from Verticillium dahliae on cotton

“…Verticillium dahliae mutants-lacking VMK1 (a mitogen-activated protein kinase gene) have been observed to significantly reduce microsclerotium formation and decreased pathogenicity on diverse hosts (Rauyaree et al 2005). The sucrose non-fermenting one gene (VdSNF1), which regulates catabolic repression, is required for virulence and expression of genes involved in cell-wall degradation (Tzima et al 2011). A third useful approach is the screening of T-DNA insertional mutant libraries and the exploitation of pathogenicityrelated candidates.…”