Abstract
Water-soluble carbohydrates (WSCs) play a vital role in water stress avoidance and buffering wheat grain yield. However, the genetic architecture of stem WSCs’ accumulation is partially understood, and few candidate genes are known. This study utilizes the compressed mixed linear model-based genome wide association study (GWAS) and heuristic post GWAS analyses to identify causative quantitative trait nucleotides (QTNs) and candidate genes for stem WSCs’ content at 15 days after anthesis under different water regimes (irrigated, rainfed, and drought). Glucose, fructose, sucrose, fructans, total non-structural carbohydrates (the sum of individual sugars), total WSCs (anthrone based) quantified in the peduncle of 301 bread wheat genotypes under multiple environments (E01-E08) pertaining different water regimes, and 14,571 SNPs from “35K Axiom Wheat Breeders” Array were used for analysis. As a result, 570 significant nucleotide trait associations were identified on all chromosomes except for 4D, of which 163 were considered stable. A total of 112 quantitative trait nucleotide regions (QNRs) were identified of which 47 were presumable novel. QNRs qWSC-3B.2 and qWSC-7A.2 were identified as the hotspots. Post GWAS integration of multiple data resources prioritized 208 putative candidate genes delimited into 64 QNRs, which can be critical in understanding the genetic architecture of stem WSCs accumulation in wheat under optimum and water-stressed environments. At least 19 stable QTNs were found associated with 24 prioritized candidate genes. Clusters of fructans metabolic genes reported in the QNRs qWSC-4A.2 and qWSC-7A.2. These genes can be utilized to bring an optimum combination of various fructans metabolic genes to improve the accumulation and remobilization of stem WSCs and water stress tolerance. These results will further strengthen wheat breeding programs targeting sustainable wheat production under limited water conditions.
Highlights
Current photosynthates and the photosynthates reserved in various vegetative tissues are two primary carbon sources for developing grain in wheat
We have identified a substantial number of 382 quantitative trait nucleotides (QTNs) delimited into 112 quantitative trait nucleotide regions (QNRs) for the six targeted traits; many of which are endorsed by previous genome wide association study (GWAS) and bi-parental QTL mapping on stem water-soluble carbohydrates (WSCs)
The functional enrichment analysis followed by functional group-based networking (Figures 6A,B) of hub genes left us with the information on the interaction of various functional groups interacting with major fructans metabolic genes, which we reported in QNRs qWSC-4A.2 and qWSC-7A.2, and other sugar metabolic genes, in a complex and coordinated network
Summary
Current photosynthates and the photosynthates reserved in various vegetative tissues are two primary carbon sources for developing grain in wheat. When photosynthesis is absent during the dark period or depressed due to senescence and/or hostile growth conditions, developing grains become more dependent on the redistributed reserved photosynthates for their carbon requirement (Schnyder, 1993). Fructose, sucrose, and fructans are primary WSCs in wheat plants, which redistribute as a significant carbon source under depressed photosynthesis. Sucrose signaling pathways leading to fructans and anthocyanin accumulation play a significant role in abiotic and biotic stress (Van den Ende and El-Esawe, 2014). Fructans protect the plants by maintaining membrane stability and reducing osmotic potential (Valluru and Van Den Ende, 2008; Livingston et al, 2009). The role of fructans in reactive oxygen species (ROS) scavenging mechanisms and phloemmobile signaling has been proposed in plants under waterstressed conditions (Peshev et al, 2013; Van den Ende, 2013)
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