BPM Proteins Modulate Heat Stress Response in Arabidopsis thaliana Seedlings

Plant responses to heat stress include complex transcriptional networks and protein regulations in which BTB/POZ-MATH (BPM) proteins participate as a part of ubiquitin-mediated protein degradation. Arabidopsis thaliana contains six BPM genes involved in responses to environmental changes, including heat. Seedlings overexpressing BPM1 (oeBPM1), seedlings with downregulation of BPM1, 4, 5, and 6 (amiR-bpm) and wild type were exposed to 37 °C for 6 h. Treatment caused stronger decline of photosynthesis in oeBPM1 than in amiR-bpm and wild type, although all seedlings recovered after 24 h at 24 °C. The activity of the antioxidant enzymes catalase, guaiacol peroxidase, and ascorbate peroxidase remained unchanged in oeBPM1, but increased in amiR-bpm and wild type. Heat stress induced HSP70 and HSP90 in all seedlings but expression remained notably higher in amiR-bpm after recovery. DREB2A and HSFA3 expression increased in all seedlings immediately after stress, with the strongest induction in amiR-bpm. In amiR-bpm and wild type, BPM2 expression was induced immediately after exposure, while BPM1, BPM3, BPM4, and BPM6 were upregulated in wild type after recovery. In oeBPM1 seedlings, BPM4 expression decreased and BPM6 expression increased immediately after treatment at 37 °C for 6 h. The results suggest that BPM proteins modulate heat stress response by influencing photosynthesis, activation of antioxidant enzymes, accumulation of HSPs, and expression of heat-responsive genes, thus contributing to the different physiological strategies observed in A. thaliana lines with altered expression of BPM genes.