Identification and Expression Analysis of the CsMYB Gene Family in Root Knot Nematode-Resistant and Susceptible Cucumbers

MYB (myeloblastosis) transcription factors (TFs) play important roles in controlling various physiological processes in plants, such as responses to biotic and abiotic stress, metabolism, and defense. A previous study identified a gene, Csa6G410090, encoding a plant lipid transfer protein (LTP), as a possible regulator in cucumber (Cucumis sativus L.) of the resistance response to root-knot nematode (RKN) [Meloidogyne incognita Kofoid and White (Chitwood)]. Myb-type DNA-binding TFs were presumed to regulate downstream genes expression, including LTPs, however, the regulation mechanism remained unclear. To elucidate whether and which MYB TFs may be involved in regulation of the resistance response, this study identified 112 genes as candidate members of the CsMYB gene family by combining CDD and SMART databases, using the Hidden Markov Model (HMM) and manual calibration. Within this group, ten phylogenetic subgroups were resolved according to sequence-based classification, consistent with results from comprehensive investigation of gene structure, conserved motifs, chromosome locations, and cis-element analysis. Distribution and collinearity analysis indicated that amplification of the CsMYB gene family in cucumber has occurred mainly through tandem repeat events. Spatial gene expression analysis showed that 8 CsMYB genes were highly expressed at differing levels in ten different tissues or organs. The roots of RKN-resistant and susceptible cucumbers were inoculated with M. incognita, finding that CsMYB (Csa6G538700, Csa1G021940, and Csa5G641610) genes showed up-regulation coincident with upregulation of the “hub” gene LTP (Csa6G410090) previously implicated as a major gene in the resistance response to RKN in cucumber. Results of this study suggest hypotheses regarding the elements and regulation of the resistant response as well as possible RKN resistance-enhancing strategies in cucumber and perhaps more broadly in plants.