The stimulatory effect of Thuricin 17, a PGPR-produced bacteriocin, on canola (Brassica, napus L.) germination and vegetative growth under stressful temperatures

Abstract

Exposure to unfavorable conditions is becoming more frequent for plants due to climate change, posing a threat to global food security. Stressful temperature, as a major environmental factor, adversely affects plant growth and development, and consequently agricultural production. Hence, development of sustainable approaches to assist plants in dealing with environmental challenges is of great importance. Compatible plant-microbe interactions and signal molecules produced within these interactions, such as bacteriocins, could be promising approaches to managing the impacts of abiotic stresses on crops. Although the use of bacteriocins in food preservation is widespread, only a small number of studies have examined their potential in agriculture. Therefore, we studied the effect of three concentrations of Thuricin17 (Th17), a plant growth-promoting rhizobacterial signal molecule produced by Bacillus thuringiensis, on germination and vegetative growth of canola (Brassica napus L.) under stressful temperatures. Canola responded positively to treatment with the bacterial signal molecule under stressful temperatures. Treatment with 10 -9 M Th17 (Thu2) was found to significantly enhance germination rate, seed vigor index, radical and shoot length and seedling fresh weight under low temperature, and this treatment reduced germination time which would be an asset for higher latitude, short growing season climates. Likewise, Thu2 was able to alleviate the adverse effects of high temperature on germination and seed vigor. Regarding vegetative growth, interestingly, moderate high temperature with the assistance of the compound caused more growth and development than the control conditions. Conversely, low temperature negatively affected plant growth, and Th17 did not help overcome this effect. Specifically, the application of 10 -9 (Thu2) and 10 -11 M (Thu3) Th17 had a stimulatory effect on height, leaf area and biomass accumulation under above-optimal conditions, which could be attributed to modifications of below-ground structures, including root length, root surface, root volume and root diameter, as well as photosynthetic rate. However, no significant effects were observed under optimal conditions for almost all measured variables. Therefore, the signal compound tends to have a stimulatory impact at stressful temperatures but not under optimal conditions. Hence, supplementation with Th17 would have the potential as a plant growth promoter under stressed circumstances.

Mitigation of drought or a combination of heat and drought stress effects on canola by Thuricin 17, a PGPR-produced compound

“…A similar conclusion, distinct responses to different concentrations of bacterial compounds, was reached by other studies (Schwinghamer et al, 2015(Schwinghamer et al, , 2016Naamala et al, 2022). A clear example of this was observed in our previous study when three different concentrations of Th17, 10 −7 , 10 −9 , and 10 −11 M, were applied, and nanomolar of Th17 was the most effective in enhancing seed germination, seedling growth, and vegetative growth under stressfully high temperatures (Nazari et al, 2022). Our findings are consistent with the work of Schwinghamer et al (2016) regarding the application of different levels of two microbial compounds, LCO and Th17, which indicated concentration-dependent behavioral responses under various growth conditions and development stages.…”

“…Additionally, for foliar experiments, across all conditions, no meaningful changes were observed due to the application of the compound. Our previous studies have indicated positive effects of treating canola seeds and root drenching with 10 −9 and 10 −11 M Th17, which caused germination increases, germination time reduction, and longer radicals under moderately high temperature and optimal conditions (Nazari et al, 2022). Similar root development effects on soybean have been reported for this plant growth regulator under salt stress and this was associated with changes in the level of ABA (Prudent et al, 2015).…”

“…Th17 levels were applied either as a pre-planting seed treatment followed by root drench or spray at the time of stress. For the seed treatment experiments, seeds were soaked in 10 ml of two concentrations of Th17, 10 −9 and 10 −11 M, suggested from germination data analysis (Nazari et al, 2022), and distilled water as a control, which was followed by weekly root drenching of the compound (three times in total) until stress induction time (based on the initial experiments), while Th17 solutions and distilled water were sprayed on leaves with an atomizer just prior to stress induction for foliar experiments. For leaf sprays, Tween 20 (0.01%) was added as a surfactant to treatment solutions, including the control.…”

“…Canola seeds were placed in 10 cm pots filled with AGRO MIX R G10 media. The plant growth chamber (Conviron R, Canada) conditions were as follows: 22/18 • C day/night, photoperiod of 14/10 h light/darkness cycle, 60%−70% relative humidity, and photosynthetic irradiance of 350-400 µmol m −2 s −1 (Nazari et al, 2022). The plants were trimmed to one seedling per container after a week.…”

“…This signal molecule was partially sequenced by Gray et al (2006b) and its full sequence was eventually determined (Lee et al, 2009). The molecular weight of Th17 is low, 3.162 kDa, and this compound is highly resistant to heat and pH (range of 1.0-9.25) with anti-microbial activity and plant growth promotion capacity, particularly under stressful conditions (Jung et al, 2011;Prudent et al, 2015;Schwinghamer et al, 2016;Subramanian et al, 2016;Nazari and Smith, 2020;Nazari et al, 2022). We should add that the most recent characterization of Th17 has revealed differences from our initial understating; hence we are considering renaming it Bacillin 20.…”