Abstract
BackgroundMitogen-activated protein kinase (MAPK) cascades play a crucial role in plant growth and development as well as biotic and abiotic stress responses. Knowledge about the MAPK gene family in cotton is limited, and systematic investigation of MAPK family proteins has not been reported.ResultsBy performing a bioinformatics homology search, we identified 28 putative MAPK genes in the Gossypium raimondii genome. These MAPK members were anchored onto 11 chromosomes in G. raimondii, with uneven distribution. Phylogenetic analysis showed that the MAPK candidates could be classified into the four known A, B, C and D groups, with more MAPKs containing the TEY phosphorylation site (18 members) than the TDY motif (10 members). Furthermore, 21 cDNA sequences of MAPKs with complete open reading frames (ORFs) were identified in G. hirsutum via PCR-based approaches, including 13 novel MAPKs and eight with homologs reported previously in tetraploid cotton. The expression patterns of 23 MAPK genes reveal their important roles in diverse functions in cotton, in both various developmental stages of vegetative and reproductive growth and in the stress response. Using a reverse genetics approach based on tobacco rattle virus-induced gene silencing (TRV-VIGS), we further verified that MPK9, MPK13 and MPK25 confer resistance to defoliating isolates of Verticillium dahliae in cotton. Silencing of MPK9, MPK13 and MPK25 can significantly enhance cotton susceptibility to this pathogen.ConclusionsThis study presents a comprehensive identification of 28 mitogen-activated protein kinase genes in G. raimondii. Their phylogenetic relationships, transcript expression patterns and responses to various stressors were verified. This study provides the first systematic analysis of MAPKs in cotton, improving our understanding of defense responses in general and laying the foundation for future crop improvement using MAPKs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0345-9) contains supplementary material, which is available to authorized users.
Highlights
Mitogen-activated protein kinase (MAPK) cascades play a crucial role in plant growth and development as well as biotic and abiotic stress responses
We used 20 Arabidopsis MAPK protein sequences as direct queries to screen the potential MAPKs. These predicted GrMAPK sequences were confirmed by FGENESH and the conserved protein domains in their sequences were analyzed by ExPASy proteomics Server [30]
We anchored expressed sequence tag (EST) sequences for four cotton species, Gossypium hirsutum (Gh), G. barbadense (Gb), G. arboreum (Ga) and G. raimondii (Gr), which we downloaded from the GenBank EST database
Summary
Mitogen-activated protein kinase (MAPK) cascades play a crucial role in plant growth and development as well as biotic and abiotic stress responses. One of the major ways to sustain increases in cotton production in many regions of the world affected by abiotic and biotic stresses involves mining key genes for stress tolerance improvement. Protein phosphorylation and dephosphorylation are major defense mechanisms for controlling cellular functions in response to external signals. The mitogen-activated protein kinase (MAPK) cascade is one of the universal signaling pathways involved in responses to external stimuli [2,3,4,5,6]. As the last component of the MAPKKK-MAPKKMAPK cascade, MAPK plays crucial roles in signal transduction of extracellular stimuli in eukaryotes by phosphorylating various downstream targets [8,9,10]
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