The brassinosteroid biosynthesis enzyme gene PeCPD improves plant growth and salt tolerance in Populus tomentosa

Abstract

Abstract A major challenge in the development of novel industrial woody crops lies in the trade-offs underlying plant growth, wood quality and abiotic stress tolerance. Single gene modifications in perennial species often lead to improvements in only one of these three processes. However, brassinosteroids (BRs) affect these three aspects, thus a BRs biosynthesis enzyme gene, PeCPD (Populus euphratica Oliv. Constitutive Photomorphogenenic Dwarf), was selected for this goal. PeCPD was mainly expressed in stems and leaves, and showed rapid responses to salt treatment. Plant height and biomass were improved in the PeCPD overexpressed lines, which was accompanied by the promotion of xylem differentiation and the reduction of pith size, consequently improving timber quality, relative to the wild type Populus tomentosa Carr. The transgenic lines also showed higher salt tolerance relative to the wild type, as indicated by less visual injuries and lower reactive oxygen species pressure. This was partly due to increased levels of soluble protein as well as higher superoxide dismutase (SOD) activity and proline level. Our results demonstrated the PeCPD overexpression mediates the trade-off between growth and abiotic stress adaptation in woody plants. The PeCPD overexpression modified the gene expression of BRs biosynthesis and metabolic process, which enhanced BRs response as indicated by improved transcript level of BRs signaling component. Our results showed that modifying PeCPD has a great potential for jointly improving growth, timber quality and abiotic stress tolerance in woody plants.