Abstract
Mitogen-activated protein kinase (MAPK) cascades have important functions in plant growth, development, and response to various stresses. The MAPKK and MAPKKK gene families in tomato have never been systematically analyzed. In this study, we performed a genome-wide analysis of the MAPKK and MAPKKK gene families in tomato and identified 5 MAPKK genes and 89 MAPKKK genes. Phylogenetic analyses of the MAPKK and MAPKKK gene families showed that all the MAPKK genes formed four groups (groups A, B, C, and D), whereas all the MAPKKK genes were classified into three subfamilies, namely, MEKK, RAF, and ZIK. Evolutionary analysis showed that whole genome or chromosomal segment duplications were the main factors responsible for the expansion of the MAPKK and MAPKKK gene families in tomato. Quantitative real-time RT-PCR analysis showed that the majority of MAPKK and MAPKKK genes were expressed in all tested organs with considerable differences in transcript levels indicating that they might be constitutively expressed. However, the expression level of most of these genes changed significantly under heat, cold, drought, salt, and Pseudomonas syringae treatment. Furthermore, their expression levels exhibited significant changes in response to salicylic acid and indole-3-acetic acid treatment, implying that these genes might have important roles in the plant hormone network. Our comparative analysis of the MAPKK and MAPKKK families would improve our understanding of the evolution and functional characterization of MAPK cascades in tomato.
Highlights
Mitogen-activated protein kinase (MAPK) cascades, which are widely distributed in eukaryotes, have an important function in the diverse developmental and physiological processes of plants, and in response to various biotic and abiotic stresses [1,2]
The existence of all MAPKKs was supported by EST hits except SlMAPKK5, and two out of five MAPKKs were found in full-length cDNA sequences
The existence of MAPKKK family genes was supported by EST hits, whereas only 11 out of 89 SlMAPKKKs were found in full-length cDNA sequences
Summary
Mitogen-activated protein kinase (MAPK) cascades, which are widely distributed in eukaryotes, have an important function in the diverse developmental and physiological processes of plants, and in response to various biotic and abiotic stresses [1,2]. MAPKKK activates MAPKK through the phosphorylation of serine and serine/threonine residues in its T-loop. MAPKK activates MAPK through the phosphorylation of tyrosine and threonine residues in the TEY or TDY motif between kinase subdomains VII and VIII. Plant MAPK cascade genes were first reported in Arabidopsis. MAPK cascade family genes have been identified in many other plant species, including poplar, rice, soybean, maize, tomato and N. benthamiana [3,4,5,6,7,8,9,10,11,12]
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