PNNL

Abstract

Abiotic stress can cause significant damage to plants, including detrimental effects on the sustainable production of bioenergy woody crops. Since specific promoters control the expression of stress resistance genes, promoter engineering has been proposed as a promising solution to overcome the challenges caused by various abiotic stressors. Through previous studies, we synthesized 6 osmotic-responsive promoters (SD9-1, SD9-2, SD9-3, SD13-1, SD18-1, and SD18-3) from poplar transcriptome data using a de novo DNA-motif-detecting algorithm (Yang et al. 2021). Their stress inducibility was identified in water-deficit and salt treatment assays using poplar leaf mesophyll protoplast transformation and agroinfiltration of Nicotiana benthamiana leaves. In this study, these 9 synthetic promoters were stably transformed into the Populus tremula ? Populus alba hybrid poplar (INRA 717-1B4), by which GFP inducibility was screened under osmotic stress conditions. Of 6 transgenic poplar lines each harboring a different synthetic promoter, SD18-1, 9-2, and 9-3 promoters showed significant induction of GFP expression in both salt and osmotic-stress treatments. Each synthetic promoter employed heptamerized repeats of specific cis-regulatory elements. The entire SD9 motif-repeated version did not activate stronger downstream GFP induction than the shorter promoters consisting of heptamerized SD9-1, 9-2, and 9-3 (partial SD9 motifs). This result implies that shorter synthetic promoters (~50 bp) with versatility in transgenic poplar. The tested promoters will be employed to develop stress-responsive bioenergy tree crops in the future, empowering poplar and other woody plant species to more efficiently serve as valuable resources for sustainable biomass feedstock production.