ABSTRACT
When fungal pathogens invade plant tissues, some new proteins appear and accumulate in the
infected tissues. These proteins are called pathogenesis-related (PR) proteins, because they
appear during pathogenesis (Vidhyasekaran, 2004, 2007). PR proteins are defined as proteins
encoded by a host plant’s genome that are induced specifically in pathological situations
(Vidhyasekaran, 2002). Van Loon et al. (1994) suggested that to call a protein as a PR protein,
the protein has to be newly expressed upon infection. This seems to be the most important
criterion to define a PR protein (Van Loon, 1999). These PR proteins have been detected during
pathogenesis in almost all plant species so far studied (Funnell et al., 2004; Piggott et al., 2004;
Coram and Pang, 2005; Espino et al., 2005; Ito et al., 2005; Rodrigues et al., 2005; Sante´n et al.,
2005; Wang et al., 2005; Wilkinson et. al., 2005; Makandar et al., 2006). PR proteins are induced
not only by fungal pathogens (Faize et al., 2004; Funnell et al., 2004; Wang et al., 2005), but also
induced by viral (Gordon-Weeks et al., 1997), bacterial (Strobel et al., 1996; Vidal et al., 1997),
and viroid (Garcia Breijo et al., 1990; Domingo et al., 1994) pathogens. Besides these pathogens,
insect pests (Fidantsef et al., 1999) and nematodes (Rahimi et al., 1996) also induce PR proteins.
