Role of Pathogenic Genes of Fusarium oxysporum, Coding Cell Wall Degrading Enzymes during Wilt Infection in Plants - Biotechnology of Fungal Genes - page 262

makes up a signifi cant part of the hemicellulose fraction of the plant cell
wall (Wong et al. 1988, Ruiz-Roldán et al. 1999). The presence of xylanases
in F. oxysporum was previously reported (Jones et al. 1972, Ruiz-Roldán et
al. 1997, Ondøej et al. 2008) . In F. oxysporum f.sp . lycopersici, four xylanase
genes (Xyl2, Xyl3, Xyl4 and Xyl5) have recently been identifi ed (Ruiz-Roldán
et al. 1999, Gómez- Gómez et al. 2001, 2002). To degrade cellulose, cellulase
enzymes C1 and C2 act upon native, insoluble cellulose to produce linear
chains that are subsequently attacked by the cellulase enzyme Cx to produce
cellobiose and glucose (MacHardy and Beckman 1981). Fusarium produces
both Cx and C1 enzymes (Husain and Dimond 1960). Pectate lyases (Pels)
catalyse the trans-elimination of pectate (Linhardt et al. 1986). No effect on
the virulence of F. oxysporum f.sp . lycopersici was found when knocking out
an individual Pel gene (Di Pietro et al. 2003). The simultaneous disruptions
of two Pel genes, however, drastically reduced virulence in F. oxysporum
f. sp. pisi (Rogers et al. 2000, Huertas-González et al. 1999). CWDEs and
other virulence factors in F. oxysporum are transcribed by virulence genes.
Seventeen virulence genes have already been characterized in F. oxysporum
(Roncero et al. 2003). One of these genes produces proteins that proved
to be of great importance in disease development. These proteins are the
mitogen-activated protein kinase (MAPK) (Di Pietro et al. 2001). MAPKs are
involved in transducing a variety of extracellular signals and for regulating
growth and differentiation processes in eukaryotic cells (Nishida and Gotoh
1993, Dickman and Yarden 1999, Schaeffer and Webber 1999, Nicolas and
Antonio 2010). Di Pietro et al. (2001) identifi ed the gene fmk1 that encodes a
MAPK in F. oxysporum. This gene is related to formation of infection hyphae,
root attachment and invasive growth by F. oxysporum f. sp. lycopersici on
tomato plants (Di Pietro et al . 2001). Chitin synthases (CHS) are the enzymes
implicated in chitin synthesis, and in fungi, they constitute a great family of
isozymes grouped into two divisions that branch into seven classes based
on amino acid sequence similarities (Munro and Gow 2001, Ruiz-Herrera
et al. 2002). Furthermore, each fungal species contains a number of CHS
genes belonging to different divisions and classes (Ruiz-Herrera et al . 2002,
Yolanda et al. 2010). In the tomato pathogen Fusarium oxysporum f. sp.
lycopersici , fi ve genes implicated in chitin synthesis, CHS1, CHS2, CHS3,
CHS7, and CHS V, have been isolated and characterized (Madrid et al. 2003,
Udíroz et al. 2004, ). CHS1, CHS2, CHS3, and CHS V belong to classes I, II,
III and V, respectively. In F. oxysporum , an intact cell wall structure has been
implicated in the plant-host interaction (Schoffelmeer et al. 1999, Yolanda
et al. 2010). In fact, chitin has been shown to play an important role in
the pathotypic behavior toward tomato plants ( Lycopersicon esculentum ).
Thus, the absence of class V CHS demonstrates that this enzyme plays
different roles in the pathogenesis of plant systems. Interestingly, recent
studies indicate the importance of the myosin motor-like CHS, exclusive to