Necrotrophic fungal infection affects indolic glucosinolate metabolism in Brassica rapa

Brassica species contains sulfur-containing secondary compounds including glucosinolates which might protect plants from pathogens. In the present investigation, the first leaves of Brassica rapa were grown in different situations such as sulfate-sufficient and deprived conditions, and infected with two types of fungi namely, Alternaria brassicicola and Botrytis cinerea as the specialist Brassica pathogen and generalist pathogen, respectively. The glucosinolates level was locally increased mainly due to indolic glucosinolates when the plant was infected with both fungi. This increase was in line with the increase in the expression of the genes including CYP79B2, CYP79B3, and CYP83B1 which are responsible for the biosynthesis of indolic glucosinolates and their regulation (MYB34 and MYB51). However, the locally induced indolic glucosinolates in plants infected with A. brassicicola were substantially higher than those of the plants infected with B. cinerea. The expression of the genes responsible for the biosynthesis of indolic glucosinolates was increased by infection of plant with A. brassicicola. The increase in the content of indolic glucosinolate occurred in the second leaf and roots, demonstrating a systemic response to fungal infection. Upon infection of plants with fungi, the content of both glucosinolates was reduced, while the expression of the most genes responsible for the biosynthesis of indolic glucosinolates was enhanced in plants infected with A. brassicicola. This may indicate that indolic glucosinolates are important in response to necrotrophic fungi in Brassica.