Abstract
MAPK cascades are universal signal transduction modules and play important roles in plant growth, development and in response to a variety of biotic and abiotic stresses. Although MAPKs and MAPKKs have been systematically investigated in several plant species including Arabidopsis, rice and poplar, no systematic analysis has been conducted in the emerging monocot model plant Brachypodium distachyon. In the present study, a total of 16 MAPK genes and 12 MAPKK genes were identified from B. distachyon. An analysis of the genomic evolution showed that both tandem and segment duplications contributed significantly to the expansion of MAPK and MAPKK families. Evolutionary relationships within subfamilies were supported by exon-intron organizations and the architectures of conserved protein motifs. Synteny analysis between B. distachyon and the other two plant species of rice and Arabidopsis showed that only one homolog of B. distachyon MAPKs was found in the corresponding syntenic blocks of Arabidopsis, while 13 homologs of B. distachyon MAPKs and MAPKKs were found in that of rice, which was consistent with the speciation process of the three species. In addition, several interactive protein pairs between the two families in B. distachyon were found through yeast two hybrid assay, whereas their orthologs of a pair in Arabidopsis and other plant species were not found to interact with each other. Finally, expression studies of closely related family members among B. distachyon, Arabidopsis and rice showed that even recently duplicated representatives may fulfill different functions and be involved in different signal pathways. Taken together, our data would provide a foundation for evolutionary and functional characterization of MAPK and MAPKK gene families in B. distachyon and other plant species to unravel their biological roles.
Highlights
The mitogen activated protein kinases (MAPK) pathway is conserved in evolution through the plant and animal kingdoms
Based on Arabidopsis MAPK and MAPKK nomenclature suggestions [27], each gene was named with a two-letter code corresponding to B. distachyon (Bd), followed the family designation (MPK or MKK), and a number (Table 1)
The results revealed that the activation loop motif of four members of the ‘Group D’ (OsMKK4, OsMKK5, BdMKK4 and BdMKK5) and all the members of ‘Group C’ was either absent or located 3–5 residues downstream of the canonical position (Figure 3), especially the BdMKK10-1, BdMKK10-3, BdMKK10-4, BdMKK10-5 and OsMKK10-3 which were more divergent in the S/ T-X5-S/T motif compared with others
Summary
The mitogen activated protein kinases (MAPK) pathway is conserved in evolution through the plant and animal kingdoms. These proteins have been implicated in diverse cellular processes including cell growth, proliferation, differentiation, survival, development and in responses to a diversity of environmental stimuli including cold, heat, reactive oxygen species, UV, drought and pathogen attack [1,2,3,4]. MAPKKKs are serine/threonine kinases phosphorylating two amino acids in the S/T-X3–5-S/T motif of the MAPKK activation loop. MAPKKs are dual-specificity kinases that activate a MAPK through double phosphorylation of the T-X-Y motif in the activation loop (T-loop). The activated MAPK leads to the phosphorylation of transcription factors and other signaling components that regulate the expression of downstream genes [5]
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