Functional characterisation of cell wall-associated β-glucanases and peroxidase induced during wheat-Diuraphis noxia interactions

Abstract

Wheat plants infested by Russian wheat aphids (RWA) induce a cascade of defence responses, which include increased activity of β-1,3-glucanase and peroxidase (POD). There is a lack of information regarding β-1,3-glucanase and POD synergistic effects on the plant cell wall modification and characterisation during wheat-RWA infestation. This study aimed to characterise the physicochemical properties of the cell wall-bound POD and β-1,3-glucanase during RWA-wheat interaction. The susceptible Tugela, moderately resistant Tugela-Dn1, and resistant Tugela-Dn5 cultivars were planted in a glasshouse to a seedling stage before being infested with RWASA2 for 14 days. The findings showed a significant increase in β-1,3-glucanase and POD activities in the infested Tugela-Dn5 and Tugela-Dn1 cultivars over the 14 days. However, in the Tugela enzymes were repressed. In addition, it was shown for the first time that β-1,3 − 1,4-glucanase activity specific toward mixed-linked glucan was significant in the resistant cultivar over 14 days. β-1,3-glucanase, β-1,3 − 1,4-glucanase and POD displayed optimum at pH 5. β-1,3-glucanase and POD displayed temperature optimum at 40 and 50 °C, respectively. However, β-1,3 − 1,4-glucanase had temperature optimum at 25 °C. β-1,3-glucanase and POD had a thermo-stability at 37 °C followed by about 80% relative activity at 70 °C, but β-1,3 − 1,4-glucanase displayed thermostability at 25 °C and retained more than 75% at 70 °C, confirming that β-1,3 − 1,4-glucanase and β-1,3-glucanase induced in the resistant cultivars cell wall were two different enzymes. Mechanism of actions and oligosaccharide displayed that β-1,3-glucanase was highly active against β-1,3-glucan and required a triose and higher oligosaccharide to be active. Our findings demonstrated cell-wall bound POD and β-1,3-glucanase activities significantly increased in wheat after RWASA2 infestation, revealing they acted synergistically to reinforce the cell wall to deter RWASA2 feeding in resistant cultivars.