Genome-wide analysis of bHLH transcription factor and involvement in the infection by yellow leaf curl virus in tomato (Solanum lycopersicum)

Abstract

Background: The basic helix-loop-helix (bHLH) proteins are a superfamily of transcription factors that can bind to specific DNA target sites. They have been well characterized in model plants such as Arabidopsis and rice and have been shown to be important regulatory components in many different biological processes. However, no systemic analysis of the bHLH transcription factor family has yet been reported in tomatoes. Tomato yellow leaf curl virus (TYLCV) threatens tomato production worldwide by causing leaf yellowing, leaf curling, plant stunting and flower abscission. Results: A total of 152 bHLH transcription factors were identified from the entire tomato genome. Phylogenetic analysis of bHLH domain sequences from Arabidopsis and tomato facilitated classification of these genes into 26 subfamilies. The evolutionary and possible functional relationships revealed during this analysis are supported by other criteria, including the chromosomal distribution of these genes, the conservation of motifs and exon/intron structural patterns, and the predicted DNA binding activities within subfamilies. Distribution mapping results showed bHLH genes were localized on the 12 tomato chromosomes. Among the 152 bHLH genes from the tomato genome, 96 bHLH genes were detected in the TYLCV-susceptible and resistant tomato breeding line before (0 dpi) and after TYLCV (357 dpi) infection. As anticipated, gene ontology (GO) analysis indicated that most bHLH genes are related to the regulation of macromolecule metabolic processes and gene expression. Only four bHLH genes were differentially expressed between 0 and 357 dpi. Virus-induced gene silencing (VIGS) of one bHLH genes SlybHLH131 in resistant lines can lead to the cell death. Conclusion: In the present study, 152 bHLH transcription factor genes were identified. One of which bHLH genes, SlybHLH131, was found to be involved in the TYLCV infection through qRT-PCR expression analysis and VIGS validation. The isolation and identification of these bHLH transcription factors facilitated clarification of the molecular genetic basis for the genetic improvement of tomatoes and the development of functional gene resources for transgenic research. In addition, these findings may aid in uncovering an unexplored mechanism during the TYLCV infection in tomatoes.