Abstract
Soybean is most often grown under rainfed conditions and negatively impacted by drought stress in the upper mid-south of the United States. Therefore, identification of drought-tolerance traits and their corresponding genetic components are required to minimize drought impacts on productivity. Limited transpiration (TRlim) under high vapor pressure deficit (VPD) is one trait that can help conserve soybean water-use during late-season drought. The main research objective was to evaluate a recombinant inbred line (RIL) population, from crossing two mid-south soybean lines (“Jackson” × “KS4895”), using a high-throughput technique with an aquaporin inhibitor, AgNO3, for the TRlim trait. A secondary objective was to undertake a genetic marker/quantitative trait locus (QTL) genetic analysis using the AgNO3 phenotyping results. A set of 122 soybean genotypes (120-RILs and parents) were grown in controlled environments (32/25-d/n °C). The transpiration rate (TR) responses of derooted soybean shoots before and after application of AgNO3 were measured under 37°C and >3.0 kPa VPD. Then, the decrease in transpiration rate (DTR) for each genotype was determined. Based on DTR rate, a diverse group (slow, moderate, and high wilting) of 26 RILs were selected and tested for the whole plant TRs under varying levels of VPD (0.0–4.0 kPa) at 32 and 37°C. The phenotyping results showed that 88% of slow, 50% of moderate, and 11% of high wilting genotypes expressed the TRlim trait at 32°C and 43, 10, and 0% at 37°C, respectively. Genetic mapping with the phenotypic data we collected revealed three QTL across two chromosomes, two associated with TRlim traits and one associated with leaf temperature. Analysis of Gene Ontologies of genes within QTL regions identified several intriguing candidate genes, including one gene that when overexpressed had previously been shown to confer enhanced tolerance to abiotic stress. Collectively these results will inform and guide ongoing efforts to understand how to deploy genetic tolerance for drought stress.
Highlights
Plant photosynthesis and transpirational rates are highly coupled (Sinclair, 2017)
Within the qLT_Gm12_1 quantitative trait locus (QTL) region associated with differential leaf temperature (LT) (Gm12:6971475.11867391, Table 7 and Supplementary Table 1), we identified a total of 312 genes, of which 29 were termed candidate genes based on Gene Ontologies (GOs) term and KOG annotations
Silver inhibition has been linked to the sulfhydryl group of cysteine residue of AQPs resulting in blockage of the pore for water passage (Niemietz and Tyerman, 2002)
Summary
Plant photosynthesis and transpirational rates are highly coupled (Sinclair, 2017). Most of the water lost by plants under stress is due to transpiration, which is linked to stomatal opening to allow CO2 diffusion (Devi and Reddy, 2018a; Shekoofa and Sinclair, 2020). Low water availability reduces assimilate partitioning to reproductive sinks, and on a cellular level impairs cell growth and division (Blum, 2011; Sarkar, 2020; Bennett et al, 2021; Sarkar et al, 2021a) Water related stresses, such as direct drought stress and associated factors including high temperature and evaporative demand, reduce both transpiration and photosynthesis, resulting in reduced crop yield (Sinclair, 2017; Balota et al, 2021). Soybean showed a decrease in stomatal conductance between VPD of 1.0 and 2.5 kPa, differing within genotypes (Bunce, 1981)
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