Mechanism of growth amelioration of triclosan-stressed tobacco (Nicotiana tabacum) by endogenous salicylic acid

Highlights: • RNA-seq results showed that SA signalling might be involved in the response of tobacco to TCS stress. • Transgenic tobacco overexpressing a homologous of SA binding protein gene was constructed. • Transgenic tobacco with higher endogenous SA were more resistant to TCS stress. • The second transcriptome profile was obtained on transgenic samples with TCS exposure. • Several key pathways and genes associated with the tolerance of tobacco to TCS stress were suggested. Among emerging organic contaminants (EOCs), triclosan (TCS) is an antibacterial agent and frequently detected in sludge. In this study, RNA sequencing (RNA-seq) was used to obtain the first transcriptomic profile of tobacco with TCS treatment in comparison with control. The results of transcriptome profiling indicated that salicylic acid (SA) signalling pathway actively participated in the tobacco's response to TCS treatment. The accumulation of endogenous SA in transgene tobacco lines transformed with a homologous gene of SA binding protein (LcSABP) was significantly enhanced. The resistance of transgenic tobacco lines to TCS was markedly enhanced revealed by morphological and physiological indexes while the total Chl level and P_n of transgenic individuals showed about 180% and 250% higher than that of WT on average, and the accumulation of H₂O₂ and O₂⁻ induced by TCS in SABP overexpressing tobacco was 35.3%–37.3% and 53.0%–56.0% lower than that of WT. In order to further explore the mechanism of TCS tolerance in transgenic plants, RNA-seq was then performed to obtain the second transcriptomic profile between wild type and transgenic samples with TCS exposure. The results indicated that differentially expressed genes (DEGs) were most highly enriched in MAPK signalling pathway, amino acid synthesis pathway and plant hormone transduction pathway. Especially, genes encoding key proteins such as cytochrome P450, laccase, peroxidase, glycosyl transferase, glutathione S-transferase and ATP-binding cassette were considered to be related to the increased tolerance ability of transgenic tobacco to the treatment of TCS stress. This research will likely provide novel insights into the molecular mechanism of SA-mediated amelioration of TCS stress on tobacco.