Disruption of the Gene Encoding Endo-β-1, 4-Xylanase Affects the Growth and Virulence of Sclerotinia sclerotiorum

Abstract

Sclerotinia sclerotiorum (Lib.) de Bary is a devastating fungal pathogen with worldwide distribution. S. sclerotiorum is a necrotrophic fungus that secretes many cell wall-degrading enzymes (CWDEs) that destroy plant’s cell-wall components. Functional analyses of the genes that encode CWDEs will help explain the mechanisms of growth and pathogenicity of S. sclerotiorum. Here, we isolated and characterized a gene SsXyl1 that encoded an endo-β-1, 4-xylanase in S. sclerotiorum. The SsXyl1 expression showed a slight increase during the development and germination stages of sclerotia and a dramatic increase during infection. The expression of SsXyl1 was induced by xylan. The SsXyl1 deletion strains produce aberrant sclerotia that could not germinate to form apothecia. The SsXyl1 deletion strains also lost virulence to the hosts. This study demonstrates the important roles of endo-β-1, 4-xylanase in the growth and virulence of S. sclerotiorum.

Deletion of Endo-β-1,4-Xylanase VmXyl1 Impacts the Virulence of Valsa mali in Apple Tree

“…Endoxylanases are among the main CWDEs that are secreted by pathogenic fungi, and thus play a key role in pathogen invasion, establishment, and replication in the host plants ( Brito et al, 2006 ; Nguyen et al, 2011 ; Yu et al, 2016 ). The apple tree canker pathogen V. mali infects host plants through wounds, and then penetrates extensively into phloem and xylem tissues.…”

“…It is perceived that Xyn11A determines fungal virulence via its necrotizing rather than catalytic activity ( Noda et al, 2010 ). In S. sclerotiorum , a deletion mutant of endoxylanase SsXyl1 lost its virulence toward host plants; however, whether SsXyl1 has necrotizing activity is still unknown ( Yu et al, 2016 ). The two endoxylanases Xyn11A and SsXyl1 belong to the family GH11, while the biological roles of endoxylanases from family GH10 in the virulence are rarely studied.…”

“…The xylanase activity was measured by the 3,5-dinitrosali cylicacid (DNS) method as described by Yu et al (2016) with some modifications. The reaction mixture, consisting of 500 μl of samples (purified recombinant protein or culture filtrate), 2.5 ml 0.5% beechwood xylan in 50 mM sodium citrate buffer (pH 5.0), was incubated for 30 min at 50°C.…”

“…The xylanase-encoding genes are studied in some fungal pathogens to determine their role in cell wall-degradation, though most of these have nothing to do with the virulence ( Apel et al, 1993 ; Gómez-Gómez et al, 2001 ; Wu et al, 2006 ; Sella et al, 2013 ). However, endo-β-1, 4-xylanase-encoding genes xyn11A and SsXyl1 are prerequisite for virulence of Botrytis cinerea and Sclerotinia sclerotiorum on host plants, respectively ( Brito et al, 2006 ; Yu et al, 2016 ). Most of the identified genes encoding xylanases in fungal pathogens belong to the family GH11.…”

The Notorious Soilborne Pathogenic Fungus Sclerotinia sclerotiorum: An Update on Genes Studied with Mutant Analysis

“…In support of this, the deletion of Xyl1 that encoded an endo-β-1, 4-xylanase leads to a loss of pathogenicity. Interesting, growth retardation, less sclerotial formation, and dense hyphal branching were also observed in the mutant [69], suggestive of a role of xylanase in development as well.…”