Host-specific drought stress-amelioration effect of EPS-producing seed endophytes from xerophytic plant, Lactuca serriola

Abstract

Plants constitute a holobiont with diverse microbes. Significantly, the seed endophytes have the advantage that they can be vertically transmitted to the next generation. Some beneficial bacteria promote plant growth and even ameliorate biotic and abiotic stresses. Among them, the bacteria that produce the specific material, exopolysaccharide, are known to induce aggregation within the rhizosphere, further increasing the soil porosity and water retention and then ameliorating the water stress of the host plant. This plant-microbe interaction shows host-specificity depending on species or even genotype. This specificity is known to be affected by the root exudate composition of the host plant and the preference of microbes for this. However, studies on the effect of EPS-producing endophytes on drought-tolerant plants and their host-specificity are rare. In this study, we isolated and identified the seed endophytes from the xerophytic invasive plant, Lactuca serriola. All of the endophytes showed drought tolerance and produced the exopolysaccharide. We practically confirmed the effect of the isolated endophytes in our greenhouse environment and whether this stress-ameliorating effect showed host-specificity. We selected the Arabidopsis thaliana and the original host, L. serriola, with five different genotypes. We infected the isolates into seeds and then grew the plant under control and water-stress conditions. A bacterial strain identified as Kosakonia cowanii GG1 improves the shoot biomass and soil water contents of A. thaliana under stress conditions. On the other hand, various bacterial strains improve the plant biomass and soil water contents of L. serriola under stress conditions. Because soil water contents and plant biomass were strongly positively correlated with the amount of root-adhering soil, we can infer that the induced soil aggregation by infected strains further improves soil water retention and plant growth. Also, all the five different L. serriola genotypes showed distinctive patterns against each infected isolates. From these, we observed both the species- and genotype-specific stress-amelioration effect of EPS-producing seed endophytes. Additionally, we examined the preference of bacterial strain against root exudate of A. thaliana and L. serriola to confirm the background of host-specificity. Consequently, we showed the host-specific drought-stress ameliorating effect of EPS-producing seed endophytes. These results are expected to be a basis for the comprehension of the role of seed endophytes in the establishment of invasive plants in harsh environments.