Transcriptome and protein-protein interaction analysis reveals the tolerance of poplar to high boron toxicity regulated by transport and cell wall synthesis pathways

Soil contamination with high levels of boron (B) destroys the balance of the soil ecosystem, reduces crop yields and poses a potential threat to human health and safety. Hyperaccumulator plants such as poplar can be used to mitigate high B soil contamination and its negative effects. Despite having a certain level of understanding of the physiological response of poplars to high boron stress tolerance, the differences in boron accumulation efficiency among different clones and their underlying molecular mechanisms are still unclear. The effects of high B toxicity on growth, B accumulation and physiological parameters were investigated in this research to compare the high B tolerance and high B accumulation abilities of five poplar clones (717, SXY, NL895, 84 K, and T89). Then two poplar clones (SXY and T89) were selected, due to their differences in B content and accumulation under high B toxicity, for transcriptomic and protein-protein interactions (PPI) analysis. The plant biomass and root-to-shoot ratio were reduced, the leaves exhibited symptoms of chlorosis and shrinkage of high B stressed five poplar clones. Boron toxicity significantly decreased the net photosynthetic rates, disturbed the balance of redox, induced the accumulation of H₂O₂ and malondialdehyde (MDA), and caused the increase in free proline levels in roots and leaves. B accumulation was significantly increased in the high B treated new leaves. The SXY clones showed the highest B accumulation, making it a potential hyperaccumulator for B contaminated soils. The transcriptome analysis of SXY and T89 revealed differential expression of genes involved in cell wall organization, active transmembrane transporter activity, cell wall synthesis, and B transport. The analysis of PPI indicates that these proteins work together in group functions. We identified some key differentially expressed genes (DEGs) related to transport and cell wall degradation. Our findings suggest that poplar is a plant that can tolerate high levels of boron, and it is possible to select poplar clones that accumulate high levels of boron to reduce soil boron pollution. The potential candidate genes, involved in transport and cell wall synthesis, can be focused on to improve poplar tolerance to high B in future breeding programs.