Context. Drought is a common abiotic stress affecting crop yield and quality worldwide. Sugar beet (Beta vulgaris L.) is a temperate crop that contributes greatly to world sucrose production and is affected by frequent drought. MicroRNAs (miRNAs) have been demonstrated to play an important role in plant abiotic stress responses. Protein-coding genes associated with drought resistance have been identified in sugar beet; however, studies on miRNAs involved in drought stress response are lacking.

Aims. The present study focused on analysing miRNAs in sugar beet and their roles in drought stress response.

Method. Small-RNA libraries were constructed from leaves of plants subjected to drought stress and well-watered conditions. High-throughput sequencing and bioinformatics analysis were used to investigate the genome-wide quantity of miRNAs and identify possible drought response regulatory effects.

Key results. Deep sequencing identified 49 known miRNAs and 59 new miRNAs. According to the Kyoto Encyclopaedia of Genes and Genomes (KEGG), the sulfur relay system was significantly enriched under drought stress. Co-regulated pairs between miR156a-5p, novel_18 and novel_41, and their target genes BVRB_6g136190, BVRB_009610 and BVRB_6g136680 were observed, suggesting a negative feedback modulation involved in the miRNA pathways.

Conclusions. Our results indicate that certain metabolic pathways such as the sulfur relay system are activated under drought conditions.

Implications. The results aid understanding of the mechanisms of drought response at the molecular level and may enable tools to be devised that enhance drought resistance in sugar beet.