Genome-wide analysis of the plant-specific VQ motif-containing proteins in tomato (Solanum lycopersicum) and characterization of SlVQ6 in thermotolerance

The VQ motif-containing (VQ) proteins are plant-specific proteins with a conserved FxxhVQxhTG amino acid sequence, which regulate plant growth and development. Little is known, however, about the function of VQ proteins in tomato (Solanum lycopersicum). Here, a total of 26 SlVQ proteins were confirmed and characterized using a comprehensive genome-wide analysis. The SlVQ proteins all contain the conserved motif with seven variations, which are classified into eight groups (I, II, IV-VI, VIII-X). Most of them were predicted to be localized in the nucleus. Besides, a network including SlVQ proteins interaction with WRKY transcription factors (SlWRKYs) and mitogen-activated protein kinases (SlMPKs) is proposed. In addition, among the SlVQ genes, SlVQ6 was expressed in the range of organs and tissues with the highest levels and could response to different stresses. Ectopically overexpression of SlVQ6 in Arabidopsis plants decreased high temperature tolerance. RNA sequencing analysis revealed that several stress-related genes, such as HSP70-4, RD20, GolS1 and AT4g36010 were down-regulated in SlVQ6 overexpressing plants compared to these in wild-type under normal growth conditions. This study provides critical information about SlVQ genes and their encoded proteins, as well as further research on SlVQ functions in tomato growth and development.