Systemic induction of a Capsicum chinense nitrate reductase by the infection with Phytophthora capsici and defence phytohormones

The mRNA differential display technique was used to identify genes from Habanero pepper (Capsicum chinense Jacq.) seedlings whose expression is modified systemically by infection with the oomycete Phytophthora capsici L. Experiments with different oligonucleotide primer combinations revealed that no single gene was synthesised de novo. Instead, the quantitative accumulation of multiple transcripts was found. From these transcripts, levels of a nitrate reductase (Capsicum chinense nitrate reductase, CcNR), which has a high percentage of identity with other Solanaceae NRs, showed a consistent increase a few hours after inoculation (hai) with P. capsici. Reverse northern blotting revealed the existence of basal levels of CcNR transcripts in different adult tissues; however, systemic levels rose dramatically after spraying seedlings with salicylic acid (SA) and ethephon (ET) but not with methyl jasmonate (MeJa). Both P. capsici and defence phytohormones (DP) also modified NR enzymatic activity (nitrite:NAD+ oxidoreductase; EC 1.7.1.1) with similar kinetics. Because the application of DP induced and activated the CcNR differentially, it is possible that the activity of CcNR is related to a specific host defence response. ► Almost all pepper species are deathly susceptible to P. capsici. ► The in vitro infection of seedling roots with the oomycete induced an NR in the leaves of young seedlings. ► The NR was also induced by the exogenous application of SA and ET but not by MeJa. ► Both P. capsici and DP conduced to the systemic activation of an NR. ► Induction of NR by SA and ET might reflect an NR role in plant defence.