Dissecting Salt Tolerance in Soybean by Profiling Differential Physiological Responses under Salt Stress

Saline soils are common worldwide and limit the yield potential of many crops. Plants respond in a variety of ways to the stress imposed by saline soils. Plants under salt stress must first sense their surroundings and transmit a signal alerting the rest of the plant to the saline conditions. Salt tolerance in soybeans is typically defined by exclusion of chloride ions from foliar tissues. Though differences in ion uptake among soybean genotypes is well documented, the key mechanisms employed by tolerant cultivars to cope with salt stress on the whole-plant level are still largely unknown. Objectives of the current research focus on characterization of the differential physiological responses to salt stress between salt-sensitive and salt-tolerant soybean lines and detecting genetic differences which contribute to the ion exclusion mechanisms employed by salt-tolerant lines. We assessed phytohormone content of two soybean lines following salt stress and found a salt-induced accumulation of abscisic acid suggesting the involvement of this phytohormone in plant abiotic stress responses. The genotype for a newly characterized salt-tolerance gene, GmCHX1, was assessed in three salt-sensitive and three salt-tolerant soybean lines. In salt-sensitive soybeans, this cation/H+ antiporter-encoding gene is reported to contain a copia retrotransposon within its coding sequence. We detected the presence of this transposable element (TE) within three salt-sensitive lines from the U.S. soybean germplasm while this TE was not detected in the three salt-tolerant lines tested The ability of salt-tolerant soybeans to maintain chlorophyll content, stomatal conductance, and ion exclusion under salt stress demonstrates the wide variety of physiological responses involved in combating this abiotic stress. Determining the key genetic regulators of each of these responses will enable breeders to enhance the salt tolerance of soybeans and will likely contribute to overall tolerance to abiotic stresses. We show that disruption of the GmCHX1 coding sequence contributes to the ion inclusion that results in salt-sensitivity in three soybean cultivars from the United States. The functional GmCHX1 allele is a promising target for selection by breeders looking to protect the yield of future cultivars and elite lines which will probably be cultivated on salt-affected lands