Ubiquitin–Proteasome Pathway Genes Show Differential Transcriptional Responses to Excess Boron in Arabidopsis thaliana

Abstract

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.

Keywords

• ABA signaling
• Arabidopsis thaliana
• Boron toxicity
• E3 ubiquitin ligases
• Ubiquitin–proteasome system (UPS)

Arabidopsis thaliana’da Ubikuitin–Proteazom Yolağına Ait Genlerin Bor Fazlalılığına Karşı Transkripsiyonel Yanıtlarının Belirlenmesi

Abstract

Bor, bitki gelişimi için gerekli bir mikrobesin olmakla birlikte yüksek seviyelerde toksisiteye yol açabilmektedir. Bor fazlalığının protein döngüsünü arttırdığına dair kanıtlar çoğalmasına rağmen, ubikuitin-proteazom sisteminin (UPS) bor toleransına katkısı hâlâ yeterince anlaşılamamıştır. Bu çalışmada, hafif (1 mM) ve şiddetli (3 mM) bor toksitesine maruz bırakılan Arabidopsis thaliana fidelerinde on iki temel UPS-ilişkili genin, UPL5, KEG, PUB48, PUB54, HRD1A, AIRP3, OTU1, PIR1, PIR2, PAWH2, AIP2 ve HOS1, transkripsiyonel yanıtları incelenmiştir. Fenotipik incelemeye göre, doza bağlı büyüme inhibisyonu, yaprak kıvrılması ve kloroz gözlenmiştir. Gerçek zamanlı kantitatif- polimeraz zincir reaksiyonu (qRT-PCR) analizleri, HRD1A ve OTU1’in konsantrasyona bağlı şekilde güçlü biçimde indüklendiğini ve şiddetli stres altında artan PAWH2 ifadesiyle birlikte ER-ilişkili degradasyonun (ERAD) aktive olduğunu göstermiştir. AIP2 yalnızca şiddetli toksisiteye yanıt verirken, PUB48 her iki uygulamada da orta düzeyde uyarılmıştır. PUB54 ve AIRP3 kontrol ile karşılaştırıldığında nispeten stabil kalsa da transkript seviyeleri 3 mM’de belirgin şekilde artmış ve strese bağlı modülasyonla uyumlu bir görünüm sergilemiştir. PIR2, özellikle şiddetli toksisite altında belirgin bir şekilde indüklenmiş; bu durum, bora cevaben ubikitinasyon ve absisik asit (ABA) bağlantılı sinyal yolaklarındaki potansiyel rolünü desteklemektedir. Buna karşılık HOS1, hafif toksisite altında güçlü bir şekilde baskılanmış ancak şiddetli seviyelerde bazal ifadeyle benzer düzeyde kalmıştır; bu da doğrusal olmayan, bora bağlı bir düzenleyici geçişe işaret etmektedir. KEG, UPL5 ve PIR1 gibi bazı genler minimal transkripsiyonel değişim göstererek global değil seçici bir UPS aktivasyonuna işaret etmiştir. Genel olarak bulgular, bor toksitesinin özellikle ERAD-ilişkili ve ABA-ilişkili E3 ligazlar olmak üzere UPS bileşenlerinde hedefe yönelik bir yeniden şekillenmeyi tetiklediğini ortaya koymakta ve bitkilerde bor toleransına katkıda bulunabilecek yeni aday düzenleyicileri tanımlamaktadır.

Keywords

• ABA sinyallemesi
• Arabidopsis thaliana
• Bor toksisitesi
• E3 ubikuitin ligazları
• Ubikuitin–proteazom sistemi (UPS)

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