Poster: Plant-symbiont interactions

Abs # 595: Effect of jasmonic acid (JA) on nodulation of Medicago truncatula by Sinorhizobium meliloti

Presenter:	Cardoza, Vinitha J, vcardoza@uvm.edu
Authors	Cardoza, Vinitha J (A)   Mitchell, David  (A)   Harris, Jeanne  (A)
Affiliations:	(A): Dept of Botany, University of Vermont

The interaction between legume and Rhizobium results in the formation of nitrogen-fixing nodules on the roots of the host plant. Jasmonic acid (JA)-a plant hormone is known to play a role in plant defense upon pathogen and insect attack. We were interested to know if JA also plays a role in nodulation. In our study, on the symbiosis between the model legume Medicago truncatula, and the soil bacterium, Sinorhizobium meliloti, we have found that JA inhibits root growth and nodulation. When M.truncatula was grown on various concentrations of JA ranging from 0 μM to 10 μM there was a decline in the number of nodules. The question is whether JA directly affects the plant or the bacterial partner. We analyzed the effect of JA on Rhizobium by looking at the expression of the early nodulation gene nodF, and the late nodulation gene nifH. nodF encodes a biosynthetic enzyme required to synthesize the bacterial signaling molecule, Nod factor, and nifH encodes a subunit of the bacterial nitrogenase enzyme complex. The induction of nodF gene expression by the flavonoid luteolin was examined using a nodF:gus construct, and it was found that JA did not affect the growth of the bacterium nor did it inhibit the induction of nodF expression. To look for nifH expression, we used a nifH:gus construct and did not find any difference in nifH expression level, however the staining pattern was variable. The effect of JA on the expression of the early plant nodulation genes RIP1 and ENOD40 and the late gene, leghemoglobin, are being examined using reverse transcriptase PCR. The interaction between JA and nodule formation is of agricultural importance, since JA mediates plant defense responses and this study would provide an insight into the role of Jasmonic acid and legume symbiosis.