Mediator is a multiprotein complex integral to the transcription machinery, mediated by RNA polymerase II. Some Mediator subunits have been found to have critical functions in plants’ responses to abiotic stresses. However, the role of plant Mediator subunits in drought responses remains largely enigmatic. Here, we identified a Mediator subunit, RhMED15a, in roses (Rosa hybrida). Its expression was greatly and swiftly induced by dehydration treatment in the root. The promoter sequence of RhMED15a contains cis-acting elements that respond to abscisic acid (ABA) and methyl jasmonate (MeJA). In addition, the expression of RhMED15a was significantly up-regulated with ABA treatment and inversely down-regulated with MeJA treatment. Silencing RhMED15a using virus-induced gene silencing (VIGS) in roses significantly reduced drought tolerance in rose plants. This resulted in a significant increase in the malondialdehyde (MDA) level and a decreased survival rate in comparison to TRV controls. Moreover, we found that the expression of five drought-related genes, including dehydration responsive element binding factor 1B (DREB1B), responsive to desiccation stress 29A (RD29A), responsive to desiccation stress 29B (RD29B), early response to dehydration 14 (ERD14), and 9-cis-epoxycarotenoid dioxygenase 1 (NCED1), was considerably suppressed in RhMED15a-silenced plants during drought stress. Taken together, our results present that the Mediator tail module subunit RhMED15a serves as an enhancer of drought tolerance in rose, probably through the modulation of the expression of some drought-related genes.

High salinity restricts plant growth and geographic distribution. Plant intracellular Na⁺/H⁺ (NHX) antiporters have critical roles in plant development and stress response. However, the molecular functions of RmNHXs in Rosa multiflora remain unclear. In this study, we identified 11 putative RmNHXs in R. multiflora according to the genome-wide analysis. The RmNHXs were classified into three classes. Most of the RmNHXs were responsive to salt stress, with the greatest upregulation being observed in RmNHX2. RmNHX2 was localized at the tonoplast. RmNHX2 overexpression resulted in the enhanced salt tolerance in tobacco, whereas virus-induced gene silencing (VIGS) of RmNHX2 in R. multiflora elevated salt susceptibility. Under salt treatment, the transgenic tobaccos achieved less reactive oxygen species (ROS) accumulation and higher activities of antioxidant enzymes, which complied with the upregulated expressions of antioxidant genes. Moreover, RmNHX2-overexpression lines had a lower level of Na⁺, a higher level of K⁺, and a lower Na/K ratio. In contrast to the mentioned, VIGS of RmNHX2 in R. multiflora exhibited the opposite phenotype, accompanied by a compromised salt tolerance. Regarded together, these results demonstrate that RmNHX2 enhances plant salt tolerance by maintaining proper ion homeostasis, as well as by accelerating ROS scavenging.

Low temperatures are the most significant abiotic stressor for the conservation and production of Phalaenopsis in non-tropical areas. CBF/DREB1 transcription factors play an important role in the plant abiotic stress response. In this study, 31 DREB family members were identified in the Phalaenopsis genome. Expression pattern analysis showed that the expression of different PaDREB members varied among tissue sites. PaDREB1D was isolated from Phalaenopsis aphrodite, and multiple sequence alignment showed that PaDREB1D belonged to the A1 subgroup of the DREB family and was localized in the nucleus. PaDREB1D overexpression in protocorm-like bodies of Phalaenopsis reduced cell damage during low-temperature stress, increased antioxidant enzyme activity, and enhanced the low-temperature tolerance of protocorm-like bodies. The results of this study provide a theoretical basis for breeding for cold resistance and investigating the molecular mechanisms related to low-temperature responses in Phalaenopsis.