Boron is an essential micronutrient for plant growth, but at high levels it can cause toxicity. Despite increasing evidence linking excess boron to enhanced protein turnover, the contribution of the ubiquitin-proteasome system (UPS) to boron tolerance remains poorly understood. Here, the transcriptional responses of twelve key UPS-related genes, UPL5, KEG, PUB48, PUB54, HRD1A, AIRP3, OTU1, PIR1, PIR2, PAWH2, AIP2 and HOS1, were investigated in Arabidopsis thaliana seedlings exposed to mild (1 mM) and severe (3 mM) boron toxicity. According to phenotypic screening, revealed dose-dependent growth inhibition, leaf curling and chlorosis. Quantitative Real-Time- Polymerase Chain Reaction (qRT-PCR) analysis demonstrated that HRD1A and OTU1 were strongly induced in a concentration-dependent manner, together with elevated PAWH2 expression under severe stress, indicating activation of ER-associated degradation (ERAD). AIP2 responded exclusively to severe toxicity, while PUB48 showed moderate induction under both treatments. Although PUB54 and AIRP3 remained relatively stable compared with the control, their transcript levels increased substantially at 3 mM, consistent with stress-dependent modulation. PIR2 exhibited a pronounced induction under severe toxicity, supporting its potential involvement in boron-responsive ubiquitination and abscisic acid (ABA)-linked signaling pathways. HOS1 showed strong repression under mild toxicity but maintained near-baseline expression at severe levels, however suggesting a boron-dependent regulatory shift rather than linear dose responsiveness. Several genes, including KEG, UPL5 and PIR1, displayed minimal transcriptional variation, pointing to selective rather than global UPS activation. In general, findings of this study reveal that boron toxicity triggers targeted remodeling of UPS components, particularly ERAD-associated and ABA-related E3 ligases, highlighting new candidate regulators that may contribute to boron tolerance in plants.
Doğa Selin Kayıhan (Tue,) studied this question.