Wheat Mitogen-Activated Protein Kinase Pathways in Plant Defense Response

Plants are constantly exposed to a variety of abiotic stresses such as high or low temperatures, drought, or high salinity, and biotic stresses such as pathogen infection or insect attack. Plants respond to these stresses through the activation and coordination of various pathways. This activation and coordination requires the phosphorylation of proteins. To date, many kinases, phosphatases and other molecules involved m phosphorylation pathways have been characterized. Mitogen activated protein kinase (MAPK) pathway is one of the key phosphorylation pathways. This pathway consist of at least three core enzymes a MAPK, activated by a MAPK kinase, which is in turn activated by a MAPK kinase kinase. Also, programmed cell death is recognized as an essential physiological and genetic process during plant development and in response to biotic and abiotic stresses. In this study, we have identified wheat FLR and FLRS genes, which are MAPKK kinase and MAP kinase respectively, and FLRS has been further identified as an ERK-type MAPK. RT-PCR has revealed that FLR and FLRS transcript levels are not changed in salicylic acid (SA) and fumonisin B1 (FB1) treatments, suggesting that FLR and FLRS may not be involved in SA-mediated pathway, and they may not playa role in wheat response to FB1 at transcriptional level. However, western blotting analysis using anti-PTEYP antibody has indicated that ERK-type MAPKs (including FLRS) in wheat FHB resistant cultivar Frontana could be involved in the SA signaling pathway, and ERK-type MAPKs playa role in wheat defense against FB1 toxin at post-translational level. Further RT-PCR has indicated that PR1.2 may not be downstream of ERK-type MAPK pathway in wheat, and PR1.2 was unresponsive to SA treatment. Northern blotting analysis has shown that FLR and FLRS are transcriptionally up-regulated upon incompatible leaf rust challenge and Fusarium graminearum challenge, indicating that these two genes play a role in plant defense response to leaf rust and Fusarium graminearum challenges. Therefore, potentially it is possible that we could manipulate FLR and FLRS for plant disease resistance. Furthermore, SA and FB1 treatments induced cell death in wheat, which appeared to be necrosis and associated with concurrent accumulation of ROS. Further study will help delineate the pathways and function of FLR and FLRS genes in plant growth and development and in cell death regulation.