Diverse Functions of MAPK(Mitogen-activated protein kinase) Cascade Genes and Its Researches in Wheat

MAPK(Mitogen-activated protein kinase) cascade, which is composed of MAP3K, MAPKK, and MAPK, regulates the activity of diverse proteins via phosphorylation of specific amino acid residues. It is involved in a number of plant growth and development pathways and also responses to the environment. Wheat is one of the major crops worldwide, along with maize and rice. Despite its importance, its huge and complex allohexaploid genome makes it hard to investigate agronomically useful genes. With a development of Next Generation Sequencing technologies, utilization of wheat genome became easily accessible. As part of this, genome-wide identification of the wheat MAPK cascade genes have been recently conducted in many researches. We collected the gene information and organized them according to the newly announced reference genome. Seed dormancy is an important trait of winter crops affecting the yield during summer. MKK3-A was found to regulate seed dormancy in wheat and barley, and the association between MAPK and phytohormones was described. Several MAP cascade pathways concerning biotic stress tolerance have been identified in model plants, such as MAP3K-MAPKK4/5-MAPK3/6-WRKY22/29 and MAP3K1-MAPKK1/2-MAPK4-MKS1. In wheat, it was reported that TaMAPK3 and 6 are involved in biotic stress tolerance. In addition, a novel biotic stress-responsive gene TaFLRS was identified and furthermore the regulation of TaMAPK4 by microRNA was investigated recently. MAPK cascade is also known to regulate abiotic stress response. Although a number of MAPK cascade genes responsive to abiotic stresses have been identified in many plant species, little pathways have been characterized. Recently, it was found that MEKK1-MKK2-MPK4 and MKK4/5-MPK3/6 cascade regulates cold response in Arabidopsis and rice. Finally, wheat MAPK cascade gene expressions under abiotic stresses were observed using previously published RNA sequencing data.