Accumulation of jasmonic acid and oxo-phytodienoate reductase (OPR) transcripts in Arabidopsis thaliana after elicitor treatment
Plants are sessile organisms and have developed numerous defense strategies to defend against both herbivores and pathogens. Arabidopsis thaliana is a model organism that is commonly used to study, among other things, the interactions between plants and their environment including plant-herbivore and plant-pathogen interactions.
Phytohormones are responsible for plant growth and development as well as many of the chemical methods plants employ as defense. The jasmonates, a class of oxylipin-derived compounds, play an important role in plant defense response against both herbivores and fungal pathogens. One such jasmonate, jasmonic acid (JA), plays a major regulatory role in growth and development and inducible defense responses. The enzyme responsible for the conversion of 12-oxo-phtyodienoic acid (OPDA) to 3-oxo-2(2'[Z]-pentenyl)- cyclopentane-1-octanoate in the JA pathway is oxo-¬phytodienoate reducatse (OPR). There are 6 known paralogs of OPR expressed in A. thaliana with OPR3 being the form believed to be responsible for in vivo¬ reduction of OPDA to JA.
To study the effect of defense responses in A. thaliana on the accumulation of JA and OPR transcripts, we used three A. thaliana mutants (tir3, etr1, opr3) and their related background lines (Col, Ws). Alamethicin (ALA), which has been shown to be a strong inducer of JA, was used to induce defense responses.
A. thaliana plants were either in a control group or an ALA treatment group and samples were collected at 2 and 4 hours. The accumulation of JA was analyzed used GC/MS. The accumulation of OPR transcripts was analyzed using semi-quantitative RT-PCR.
A general trend toward increased level of JA accumulation in treatment groups when compared to control group was observed. The opr3 mutant, which is believed to be incapable of producing JA, when induced with ALA showed a small but detectable increase in accumulation of JA at 2 h and an accumulation of JA which was significantly larger than the control at 4 h.
A general trend toward increased OPR transcript accumulation in the treatment group was observed for all OPRs. This was in contrast to previous research, which had shown accumulation of only OPR2 and OPR3 in response to fungal pathogen infection.
Further research is needed to help elucidate the synergistic and antagonistic interactions of the many different phytohormones and their role in defense responses.