|Mb, Shine - University Of Kentucky|
|Yang, Jung-wook - University Of Kentucky|
|El-habba, Mohamed - University Of Kentucky|
|Nagyabhyru, Padmaja - University Of Kentucky|
|Fu, Da-qi - University Of Kentucky|
|Navarre, Duroy - Roy|
|Ghabrial, Said - University Of Kentucky|
|Kachroo, Pradeep - University Of Kentucky|
|Kachroo, Aardra - University Of Kentucky|
Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2016
Publication Date: 7/13/2016
Citation: Mb, S., Yang, J., El-Habba, M., Nagyabhyru, P., Fu, D., Navarre, D.A., Ghabrial, S., Kachroo, P., Kachroo, A. 2016. Cooperative functioning between phenylalanine ammonia lyase and isochorishmate synthase activities contributes to salicylic acid biosynthesis in soybean. New Phytologist. 212:613-626.
Interpretive Summary: Plant diseases reduce yield, quality, profitability and food security. Scientists with the University of Kentucky and the USDA-ARS in Prosser, Washington showed that the small molecule, salicylic acid, is involved in plant resistance to Pseudomonas and Phytophthora and that the salicylic acid (SA) is derived from two different pathways that are equally important. Suppressing either pathway abolished pathogen induced increases in SA needed for resistance. Pseudomonas infection increased activity of one pathway and suppressed the other. The role of SA in defense was complex, and its role varied depending on the type of resistant genes present in the plant. Collectively, these results demonstrate mechanisms that can be used to reduce losses to disease.
Technical Abstract: Salicylic acid (SA), an essential regulator of plant defense, is derived from chorismate via either the phenylalanine ammonia lyase (PAL), or the isochorishmate synthase (ICS) catalyzed steps. The ICS pathway is thought to be the primary contributor of defense-related SA, at least in Arabidopsis. We investigated the relative contributions of PAL and ICS to defense-related SA accumulation in soybean. We show that unlike in Arabidopsis, PAL- and ICS-pathways are equally important for pathogen-induced SA biosynthesis in soybean and interestingly knock down of either pathway shuts down SA biosynthesis. Moreover, unlike in Arabidopsis, pathogen infection in soybean is associated with the suppression of ICS gene expression. The pathogen induced biosynthesis of SA via the PAL pathway correlates inversely with phenylalanine levels. Infections with either virulent or avirulent Pseudomonas syringae and Phytophthora sojae increase SA levels. However, resistance protein-mediated response to avirulent P. sojae strains functions in an SA-independent manner. These results show that the soybean PAL and ICS pathways function cooperatively and highlight an important role for PAL in pathogen-induced SA biosynthesis.