Fine‐tuning of SUMOylation modulates drought tolerance of apple

Abstract

Summary SUMOylation is involved in various aspects of plant biology, including drought stress. However, the relationship between SUMOylation and drought stress tolerance is complex; whether SUMOylation has a crosstalk with ubiquitination in response to drought stress remains largely unclear. In this study, we found that both increased and decreased SUMOylation led to increased survival of apple ( Malus × domestica ) under drought stress: both transgenic MdSUMO2A overexpressing (OE) plants and MdSUMO2 RNAi plants exhibited enhanced drought tolerance. We further confirmed that MdDREB2A is one of the MdSUMO2 targets. Both transgenic MdDREB2A OE and MdDREB2A K192R OE plants (which lacked the key site of SUMOylation by MdSUMO2A) were more drought tolerant than wild‐type plants. However, MdDREB2A K192R OE plants had a much higher survival rate than MdDREB2A OE plants. We further showed SUMOylated MdDREB2A was conjugated with ubiquitin by MdRNF4 under drought stress, thereby triggering its protein degradation. In addition, MdRNF4 RNAi plants were more tolerant to drought stress. These results revealed the molecular mechanisms that underlie the relationship of SUMOylation with drought tolerance and provided evidence for the tight control of MdDREB2A accumulation under drought stress mediated by SUMOylation and ubiquitination.

The AP2/ERF transcription factor MdDREB2A regulates nitrogen utilisation and sucrose transport under drought stress

“…MdDREB2A was mainly expressed in roots and leaves and was induced by PEG6000 (Figure ). Subsequently, MdDREB2A ‐overexpressing apple seedlings ( MdDREB2A OE ) were obtained (Figure ), which showed improved resistance to drought stress compared to those exposed to adequate water levels (Figure 2a; Li et al, 2022). MdDREB2A OE showed increased NIR activity and total nitrogen content in both shoots and roots under drought conditions compared to the wild‐type (Figure 2b–e).…”

“…The protein stability of DREB2A in Arabidopsis is finely regulated under environmental stress. For example, MdRNF4 mediates the degradation of SUMOylated MdDREB2A via ubiquitination under drought conditions (Li et al, 2022). In this study, the GFP fluorescence signal was significantly induced by nitrate (Figure ), suggesting posttranslational regulation of MdDREB2A.…”

“…The transgenic apple plants were used as described by Li et al (2022) The full-length CDS sequences of MdDREB2A were cloned into the pGWB418 vector. The recombinant vector was expressed in Agrobacterium strain EHA105 and then transformed into GL-3 apple plants.…”

“…By contrast, the unique SUMO‐conjugating enzyme, SCE1, interacts with DREB2A and SUMOylates at its K163 residue to stabilise the DREB2A protein under heat stress in Arabidopsis (Wang et al, 2020). In apple, the SUMOylation of MdDREB2A by MdSUMO2 is recognised and ubiquitinated by MdRNF4, resulting in drought stress‐modulated degradation of MdDREB2A (Li et al, 2022). Overall, the regulation of DREB2A during abiotic stress is well established.…”

Current perspectives of ubiquitination and SUMOylation in abiotic stress tolerance in plants

“…Recent studies on Malus domestica evidenced the implication of SUMOylation in regulating DREB2A stability as a critical determinant of drought tolerance. Interestingly, it was reported that drought tolerance in apples involves a complex network of increased and reduced levels of SUMOylation and ubiquitination, respectively, where SUMOylated MdDREB2A serves as a target for RNF4-mediated ubiquitination and degradation (Li et al, 2022 ). Pepper dehydration-responsive homeobox1 domain (CaDRHB1) TF serves as a positive regulator of the desiccation stress response.…”