Abstract: 【Objective】The objective of this study is to clone ClMYB, which is a gene encoding MYB transcription factor, analyze its sequence features and expression characteristics, and to provide new insights into the understanding of the molecular mechanism in response of watermelon plants to Fusarium oxysporum f. sp. niveum infection.【Method】In a recent study, a novel EST of MYB transcription factors was obtained from data analysis of microarray and suppression subtractive hybridization (SSH) of incompatible interaction between watermelon and F. oxysporum f. sp. niveum. cDNAsequenceof the MYB was isolated and cloned using cDNA from watermelon roots with F. oxysporum f. sp. niveum infection by RT-PCR method, designated as ClMYB. The conserved domains and sequence features of ClMYB protein were analyzed by bioinformatics methods. multiple sequence alignments and a phylogenetic tree of homologous species were done between ClMYB protein and its homologous ones from other species using MEGA5.0. The subcellular localization of ClMYBwas analyzedusing fusion expression vector PYBA1332-GFP. Then ORF of the cloned gene was inserted into the expression vector pCzn1 by Nde I and Xba I digestion. The recombinant plasmid was transformed into E. coli Arctic Express system and induced expression by 0.5 mmol·L^-1 IPTG for 4 h. The expression of the fusion protein was detected by SDS-PAGE. The expression pattern of target genes in watermelon with F. oxysporum f. sp. niveum were detected by real-time fluorescent quantitative PCR (qrt-PCR).【Result】Using RT-PCR method, cDNA sequence of ClMYB (GenBank: KT751229) was cloned from watermelon (PI296341-FR) root. Sequence alignment and bioinformatics analysis revealed that the deduced amino acids of ClMYB had common characteristics of MYB transcription factors with two MYB domains of R2 and R3 at the N-terminal and highly variation at the C-terminal. Phylogenetic tree analysis suggested that the encoded protein had the closest genetic relationship with Cucumis melo MYB (GenBank: XM_008440304) and Cucumis sativus MYB (GenBank: XM_011652633). Subcellular localization results showed thatClMYB protein was located in the nucleus which belongs to a typical transcription factor. The expression of fusion protein was obtained by inducing with IPTG in E. coli and its relative molecular weight was 36 kD. qrt-PCR showed that the expression of ClMYB was induced by F. oxysporum f. sp. niveum, and appeared peak earlier and higher in PI296341-FR than Black diamond. MeJA at 50 μmol·L^-1 could significantly improve the resistance of Black diamond to F. oxysporum f. sp. niveum and induce the expression of ClMYB. In PI296341-FR, the expression of ClMYB was also induced by MeJA, while its expression level was lower than Black diamond. 【Conclusion】ClMYB is a typical R2R3-MYB transcription factor and is located in the nucleus. The expression of fusion protein was obtained by prokaryotic expression and its relative molecular weight is 36 kD. The expression of ClMYB was induced by F. oxysporum f. sp. niveum and JA. It is speculated that ClMYB may be involved in JA-mediated resistance signal transduction network of F. oxysporum f. sp. niveum. It might play an important role in disease resistance of Citrullus lanatus.

Key words: watermelon, Fusarium wilt, ClMYB transcription factor, gene cloning, expression analysis