Stepwise allelic trajectory of ETP2 underlies trade-off between UVB tolerance and submergence adaptation in Arabidopsis thaliana.

Strong UVB radiation critically restricts plant growth, yield, and distribution, while mechanisms enabling adaptation to intense UVB remain unclear. Here, we uncover that the F-box ubiquitin E3 ligase UVBT1 (also known as ETP2) is indispensable for UVB tolerance in A. thaliana. In the high-altitude Tibet accession, a distinctive 166-bp deletion in ETP2 promoter leads to the complete absence of the W-box element, thereby eliminating WRKY36-mediated transcriptional repression. This results in elevated ETP2 levels, which degrade EIN2 and activate the protective anthocyanin/flavonoid pathway. Conversely, in low-altitude accessions, which are often exposed to lower UVB and higher precipitation conditions, WRKY36-mediated repression of ETP2 stabilizes EIN2 and WRKY22, endowing the plants with submergence tolerance. Notably, aside from the Tibet-accession-specific 166-bp deletion, the geographical distribution of the promoter allelic shift from C to G near the ETP2 W-box within the 166-bp region is tightly associated with UVB radiation with increasing altitudes for the other global accessions. This allelic change also enhances WRKY36-mediated repression of ETP2, suggesting an additional stepwise adaptation process. This work thus defines the WRKY36-ETP2-EIN2/WRKY22 module as a key regulator of UVB tolerance and submergence adaptation, potentially enabling A. thaliana to adapt to environments with varying UVB and precipitation conditions.