Expression analysis of key genes of phenylpropanoid pathway and phenol profiling during Ricinus communis-Fusarium oxysporum f. sp. ricini interaction

The general phenylpropanoid metabolism generates an array of secondary metabolites and phenolic acids which imparts disease resistance in plants. Expression pattern of the key genes of phenylpropanoid pathway was studied at 0, 24 and 48 h after infection (h.a.i.) and phenolic acid profiling was carried out at 0, 24, 48 and 72 h.a.i. in the leaves of wilt infected and non- infected of both resistant and susceptible genotypes of castor. Expression analysis of PAL (phenylalanine ammonia lyase), C4H1 (cinnamate 4-hydroxylase 1) and C4H2 (cinnamate 4-hydroxylase 2) genes using RT-PCR with gene specific primers showed appreciable increase in the expression of PAL and C4H-2 gene in resistant genotypes at 48 h interval than 24 h interval compared to susceptible genotype. However, gene C4H-1 was down regulated in susceptible genotypes after 24 and 48 h.a.i. while up regulated in resistant genotypes. Phenol profiling using HPTLC showed the presence of three phenolic acids i.e. caffeic acid, ferulic acid and salicylic acid in non-infected and infected castor genotypes. Higher content of caffeic and ferulic acid was detected in infected and non-infected resistant genotypes at 0, 24 and 48 h.a.i, whereas caffeic acid was not detected in susceptible genotypes at 0 h.a.i. These results suggest the critical role of phenols in castor disease resistance.