CHALCONE SYNTHASE AND PHENYLALANINE AMMONIA-LYASE MESSENGER-RNA LEVELS FOLLOWING EXPOSURE OF SORGHUM SEEDLINGS TO 3 FUNGAL PATHOGENS

Oligonucleotide primers made complementary to conserved sequences in p henylalanine ammonialyase (PAL) and chalcone synthase (CHS) genes prev iously cloned from other species were used to amplify segments of the corresponding genes from sorghum. Greater than 70% base sequence ident ity with homologous genes confirmed that a 535 bp clone (PAL1-1) and a 620 bp clone (CHS2G) were derived from the coding regions of PAL and CHS respectively. When used to probe genomic digests, the two clones d etected 3 and 5 EcoRI fragments, respectively. One fragment for each p robe was polymorphic in the parents of a mapping population, permittin g a locus for each gene to be located on a sorghum RFLP linkage map. R NA gel blot analyses were performed on extracts from control seedlings and from seedlings challenged with either of two fungal sorghum patho gens or a pathogen of maize that elicits a hypersensitive response in sorghum. Although low levels of PAL and CHS mRNA transcripts were pres ent constitutively in the controls, both rapidly accumulated to high l evels following inoculation with the maize pathogen, Bipolaris maydis, and decreasing amounts of mRNA were apparent by 120 h post-inoculatio n. Since challenge with Sporisorium reilianum was by needle inoculatio n, an additional control of mock inoculations was included for this pa thogen. However, no differences in the amount of mRNA for either gene were detected over the sampling period, whether samples from uninocula ted, mock inoculated or spore-inoculated seedlings were tested. Differ ences in the timing and level of mRNA accumulation were detected in se edlings after inoculation with Peronosclerospora sorghi. While seedlin gs of both resistant and susceptible cultivars accumulated higher leve ls of PAL and CHS mRNA than uninoculated controls, the accumulation of mRNA in resistant cultivars was higher and longer lasting than that i n susceptible cultivars. (C) 1996 Academic Press Limited.