Enhanced Drought and Salt Stress Tolerance in Arabidopsis by Flavobacterium crocinum HYN0056T

Plant growth-promoting bacteria (PGPB) are indigenous to the plant rhizosphere and largely affect many events occurring during the plant life cycle, through either a direct or an indirect mechanism such as regulation of hormonal balance, facilitation of nutrients uptake and improvement of stress tolerance. Since drought stress, a representative abiotic stress, is one of the main reasons limiting plant growth, the identification of useful PGPB involved in drought stressresistance in plants and its application into the agricultural field could be utilized as a strategy to facilitate crop productivity. To obtain a useful PGPB that is involved in drought stress resistance, we checked the expression patterns of drought-inducible marker genes such as RD29A and RAB18 in Arabidopsis after application of 16 Flavobateria obtained from various environmental sources. After screening, a PGPB known as Flavobacterium crocinum HYN0056(T), which contributes to more than twofold upregulation of drought-inducible marker genes, was finally selected for this study. Application of HYN0056(T) enhanced the tolerance against both drought stress, possibly via induction of stomatal closure, the highly related salt stress, in the presence of HYN0056(T). Moreover, treatment of HYN0056(T) under drought and salt stresses resulted in enhanced upregulation of various drought- and salt-inducible genes in Arabidopsis. HYN0056(T) was responsible for the development of lateral roots under nonstress condition, implying that it may be involved in effective uptake of water/inorganic nutrients. Based on these results, we suggest that this bacterium could be used as a useful biocontrol agent to improve plant productivity, especially under drought/salt stress conditions.