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. <i>Arabidopsis thaliana</i> contains six <i>BPM</i> genes involved in responses to environmental changes, including heat. Seedlings overexpressing <i>BPM1</i> (<i>oeBPM1</i>), seedlings with downregulation of <i>BPM1</i>, <i>4</i>, <i>5</i>, and <i>6</i> (<i>amiR-bpm</i>) and wild type were exposed to 37 °C for 6 h. Treatment caused stronger decline of photosynthesis in <i>oeBPM1</i> than in <i>amiR-bpm</i> 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 <i>oeBPM1</i>, but increased in <i>amiR-bpm</i> and wild type. Heat stress induced HSP70 and HSP90 in all seedlings but expression remained notably higher in <i>amiR-bpm</i> after recovery. <i>DREB2A</i> and <i>HSFA3</i> expression increased in all seedlings immediately after stress, with the strongest induction in <i>amiR-bpm</i>. In <i>amiR-bpm</i> and wild type, <i>BPM2</i> expression was induced immediately after exposure, while <i>BPM1</i>, <i>BPM3</i>, <i>BPM4</i>, and <i>BPM6</i> were upregulated in wild type after recovery. In <i>oeBPM1</i> seedlings, <i>BPM4</i> expression decreased and <i>BPM6</i> 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 <i>A</i>. <i>thaliana</i> lines with altered expression of <i>BPM</i> genes.