Colletotrichum gloeosporioides infection induces differential expression of glutathione S-transferase genes in Malva pusilla

Among a collection of 840 expressed sequence tags of Malva pusilla leaves infected with Colletotrichum gloeosporioides f. sp. malvae (Cgm), a total of four different glutathione S-transferase (GST) (EC 2.5.1.18) genes were identified, each showing a different pattern of expression following infection. MpGSTU1 and MpGSTU2 were members of the class tau GSTs, MpGSTF1 was a member of the class phi GSTs, and MpGSTZ1 belonged to the class zeta GSTs. Infection by Cgm occurs by a hemibiotrophic process with an initial biotrophic phase preceding the necrotrophic phase and the appearance of symptoms. Expression of MpGSTZ1 progressively increased during infection, corresponding directly with the growth of the pathogen. Expression of MpGSTU2 was similar to that of MpGSTZ1, except for a greater increase during the late necrotrophic phase. MpGSTU1 expression remained relatively constant throughout the infection, whereas MpGSTF1 expression was induced primarily during the conversion from the biotrophic to necrotrophic phases of infection. Incubation of healthy mallow leaves in the dark resulted in decreased expression of MpGSTF1 and MpGSTU1, but not MpGSTZ1 and MpGSTU2. The differential expression patterns indicate that these mallow GST genes play a variety of roles in healthy and fungal-infected leaf tissue. The nucleotide sequences reported in this paper have been submitted to GenBank under the accession numbers AY206003, AY206001, AY206002, AY206000 and AY205999.