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In the Arabidopsis thaliana (L.) Heynh. genome, six BPM genes encode BPM proteins - specific protein adaptors of the cullin E3 ligase complex that polyubiquitinate substrate proteins as part of the ubiquitin-proteasome pathway and direct them for degradation via the 26S proteasome. Research have shown that BPM proteins not only regulate various developmental processes, but also have an important role in phenotypic and physiological adaptability and the ability of plants to survive in a changing environment. The Arabidopsis line overexpressing BPM1 gene (oeBPM1), line with downregulation of BPM1, 4, 5, and 6 (amiR bpm), and wild type (wt) were exposed to 40 °C for six hours at two developmental stages - two (2L) and eight (8L) rosette leaves. The first group of plants was exposed at 2L stage, the second at 8L stage, while the third group was exposed at both stages (2L+8L). Plant growth and chlorophyll fluorescence parameters were determined using a high-throughput plant phenotyping platform (GrowscreenChamber, Jülich Plant Phenotyping Center). The oeBPM1 showed a decrease in projected leaf area (APT) after exposure to heat stress at 2L. On the other hand, both amiR bpm and wt showed significantly lower APT than their respective controls after exposure at 8L and 2L+8L. Immediately after exposure, all lines showed an increase in the maximum quantum yield of photosystem II (Fv/Fm) at 2L, with an average of 0.77 compared with 0.75 in control plants. However, in oeBPM1 and wt stressed at 2L stage, Fv/Fm decreased to 0.76 and 0.74, respectively, over the following seven days. Heat stress applied at 8L stage increased Fv/Fm in oeBPM1 and wt to an average of 0.80 compared with 0.76 in control plants, but not in amiR bpm. Moreover, amiR bpm exposed at 2L+8L showed a significant decrease in Fv/Fm (0.74) compared with control (0.77). Biomass measurement revealed lower dry weight of oeBPM1 and amiR bpm treated at 2L and 8L stages, respectively. These results suggest that overexpression of BPM1 negatively affected the selected phenotypic traits of heat-treated Arabidopsis at the early developmental stage. Interestingly, a similar effect was observed in Arabidopsis plants with downregulated BPMs after exposure to heat stress at the adult stage. |
