Expression of specific (1→3)-β-glucanase genes in leaves of near-isogenic resistant and susceptible barley lines infected with the leaf scald fungus (Rhynchosporium secalis)

Abstract

Near-isogenic resistant and susceptible lines of barley (Hordeum vulgareL.) were inoculated with a virulent race of the causal agent of leaf scald,Rhynchosporium secalis, and the expression patterns of specific barley (1→3)-β-glucan endohydrolase (EC 3.2.1.39) isoenzymes monitored. Induction of (1→3)-β-glucanase activity occurred 1 day earlier and to higher levels in the resistant backcross line BC-200 than in the susceptible parent line. Thus, the resistant plants of this backcross line responded more rapidly to pathogen invasion than susceptible lines. The increased (1→3)-β-glucanase activity was attributable predominantly to a 2–3 day period in which mRNA transcripts of genes that encode isoenzymes GII and GI accumulated. These genes may therefore be important in the defence responses of barley backcross line BC-200 to pathogen attack. A second scald-resistant backcross line, BC-30, developed levels of (1→3)-β-glucanase similar to BC-200 upon infection, but maximal levels were reached later than in BC-200. The third resistant backcross line, BC-35, showed the same pattern of expression as the susceptible parent cultivar, Clipper. The differences in expression of (1→3)-β-glucanase between the resistant backcross lines clearly show that there are physiologically distinct modes of resistance to the scald fungus in barley, and that at least one of these is accompanied by (1→3)-β-glucanase induction.