Tanscript accumulation of the mevalonate pathway genes and enzymatic activity of HMGCoA-r and EAS in chilli CM-334 infected by the false root-knot nematode Nacobbus aberrans

Abstract

Chilli CM-334 (Capsicum annuum L.) is resistant to Phytophthora capsici Leonian, but susceptible to Nacobbus aberrans (Thorne, 1935) Thorne & Allen, 1944. Its resistance to the oomycete breaks down when the plant is co-infected by this nematode. Transcript accumulation of 3-hydroxy-3-methylglutaryl CoA reductase (HMG1, HMG2 and HMG3 isoforms), farnesyl pyrophosphate synthase (FPPS), 5-epi-aristolochene synthase (EAS) and squalene synthase (SS) genes, as well as the enzymatic activities of HMGCoA-r and EAS in roots of chilli pepper CM-334 infected and non-infected by N. aberrans were determined. Plants were inoculated with 2,000 second stage juveniles of N. aberrans. Roots were harvested at 0, 2, 7, 14 and 21 days after inoculation (dai). At all of the evaluation times, there was a significantly greater accumulation of HMG1 transcripts in plants inoculated with N. aberrans than in non-inoculated plants. In contrast, HMG2 transcripts accumulated to a greater extent only at 7 dai. The largest accumulation of HMG1 mRNA was associated with a higher HMGCoAr activity and the presence of the immature females of the nematode inside the roots. The accumulation of EAS transcripts was also significantly greater in infected roots at all times after N. aberrans inoculation but its relationship to EAS enzymatic activity was not proportional. No changes in the accumulation of HMG3 and SS mRNAs were observed. FPPS mRNA levels increased in infected plants at 21 dai. The results suggest that N. aberrans modifies the expression of some genes of the mevalonate (MEV) pathway in order to create suitable conditions for its establishment and development.