Two novel Blumeria graminis f. sp. hordei genes are induced in planta and up-regulated in mlo virulent isolates

Abstract

The differential display technique was applied to the Blumeria graminis f. sp. hordei ( Bgh)-barley interaction to identify fungal genes involved in the early stages of infection. Out of 33 cDNA fragments originally isolated, nine were confirmed by RT-PCR to represent differentially expressed Bgh genes. cDNA and genomic clones of three novel genes, BIG1, BIG2, and BIG4 ( Barley-induced gene 1, 2, and 4), were characterized. They are predicted to encode secreted proteins and to be specific for the Bgh–barley interaction. In the Bgh isolate Race I, an mlo virulent isolate, they are highly up-regulated during penetration and primary haustorium formation. Expression of the BIG1 and BIG2 genes was further analysed in two near-isogenic Bgh isolates, one mlo virulent, HL3/5, and one avirulent, GE3, during the interaction with a susceptible cultivar. In both isolates the genes are up-regulated at the appressorial stage and in HL3/5 expression increases further during penetration and primary haustorium formation. This was also observed in Race I, indicating a different regulation of BIG1 and BIG2 in mlo virulent isolates.