RhMED15a-like, a subunit of the Mediator complex, is involved in the drought stress response in Rosa hybrida.

Background: Rose (Rosa hybrida) is a globally recognized ornamental plant whose growth and distribution are strongly limited by drought stress. The role of Mediator, a multiprotein complex crucial for RNA polymerase II-driven transcription, has been elucidated in drought stress responses in plants. However, its physiological function and regulatory mechanism in horticultural crop species remain elusive.

Results: In this study, we identified a Tail module subunit of Mediator, RhMED15a-like, in rose. Drought stress, as well as treatment with methyl jasmonate (MeJA) and abscisic acid (ABA), significantly suppressed the transcript level of RhMED15a-like. Overexpressing RhMED15a-like markedly bolstered the osmotic stress tolerance of Arabidopsis, as evidenced by increased germination rate, root length, and fresh weight. In contrast, the silencing of RhMED15a-like through virus induced gene silencing in rose resulted in elevated malondialdehyde accumulation, exacerbated leaf wilting, reduced survival rate, and downregulated expression of drought-responsive genes during drought stress. Additionally, using RNA-seq, we identified 972 differentially expressed genes (DEGs) between tobacco rattle virus (TRV)-RhMED15a-like plants and TRV controls. Gene Ontology (GO) analysis revealed that some DEGs were predominantly associated with terms related to the oxidative stress response, such as 'response to reactive oxygen species' and 'peroxisome'. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment highlighted pathways related to 'plant hormone signal transduction', in which the majority of DEGs in the jasmonate (JA) and ABA signalling pathways were induced in TRV-RhMED15a-like plants.

Conclusion: Our findings underscore the pivotal role of the Mediator subunit RhMED15a-like in the ability of rose to withstand drought stress, probably by controlling the transcript levels of drought-responsive genes and signalling pathway elements of stress-related hormones, providing a solid foundation for future research into the molecular mechanisms underlying drought tolerance in rose.