QTL Analysis Of Seedling, Yield And Grain Traits Under Different Mineral Nutrition Treatments In Wheat

Wheat is one major crop and plays an important role in grain production, with the large growing area. Nitrogen (N) is often considered to be one of the three most important mineral nutrient elements limiting wheat growth. The nutrient-related traits of N metabolism and yield-related traits are complicated quantitative traits. To improve nitrogen use efficicency (NUE), an elaborate understanding of the genetic basis of traits that manifest at different stages of plant development under varying nutrient conditions is required. In wheat (Triticum aestivum L.), genotypic differences in the NUE of N have been well documented, suggesting that it is possible to improve NUE through a genetic approach. Quantitative trait locus (QTL) analysis provides an effective approach to dissect complicated traits into component loci and study their relative effects on a specific trait.In order to improve wheat breeding level and study the genetic mechanism of nitrogen use efficicency, quantitative trait locus (QTL) analysis was conducted in common wheat using a set of 131 recombinant inbred lines (RIL) derived from'Chuan 35050'×'Shannong 483'. The objective of this study was to detect QTLs at the seedling stage grown in a variety of N (P, K) concentrations in hydroponic culture trial, and at maturity under moderate, high and low N concentrations in a pot trial. Furthermore, we sought to isolate and characterize the full-length gDNA sequence of TaGS1a and identify polymorphisms among 60 wheat varieties. We also explored a functional marker based on diversities of the gDNA sequence and investigated the role of the TaGS1a in the control of NUE at the seedling stage under hydroponic culture trial and the grain traits under field trial.The mian results are as follows.(1) Nutrient use efficiency, comprising of nutrient uptake and utilization efficiency, is regarded as one of the most important factors for wheat yield. In the present study, 6 morphological, 9 nutrient content, and 9 nutrient utilization efficiency traits were investigated at the seedling stage using a set of recombinant inbred lines (RILs), under hydroponic culture of 12 treatments including single nutrient levels and two- and three-nutrient combinations treatments of N, P and K. A total of 373 quantitative trait loci (QTLs) on 18 chromosomes for the 24 traits (590 QTLs for trait-treatments) were detected. Most QTLs were located in new marker regions. Twenty-two important QTL clusters were mapped on 12 chromosomes, 1A, 1B, 1D, 2B, 3B, 4A, 4B, 5D, 6A, 6B, 7A and 7B. Of these, 5 clusters involved 214 QTLs (36.8%) for trait-treatments, indicating that these 5 loci were important for NuUE of N, P and K. We found evidence for cooperative uptake and utilization (CUU) of N, P and K in the early growth period at both phenotype and QTL level. The correlation coefficients (r) between nutrient content and nutrient utilization efficiency traits for N, P and K were almost all significantly positive correlations. A total of 33 cooperative CUU loci (L1-L33) were found, which included 277 out of the 417 QTLs (66.4%) for trait-treatments, indicating that the CUU-QTLs were common for N, P and K. The CUU-QTLs in L4, L6, L7, L15 and L17 were relatively stable. The CUU-QTLs may explain the CUU phenotype at the QTL level.(2) Twenty-one seedling traits under hydroponic culture trial of six N treatments, and 16 yield traits and grain size traits in a pot trial of three N concentrations were investigated. A total of 203 QTLs for seedling traits and 92 QTLs for yield and grain size traits were detected. Forty-seven QTL clusters were mapped, which involved 291 out of 350 QTLs (83.1%) for treatment-traits. We found cooperative uptake and utilization (CUU) of N, P and K under hydroponic culture trial at both the phenotype and QTL level. A total of 20 CUU loci were found, which included 112 out of 243 QTLs (46.1%) for treatment-traits under hydroponic culture trial. Surprisingly, 20 QTL clusters (42.6%) were referred simultaneously to seedling traits and yield or grain size traits, which should be the constitutive expression loci at the whole stage of plant growth and development. Consequently, most QTLs in this study were located in new marker regions. The founding of constitutive expression loci provided genetic evidence for that seedling traits influenced yield and grain size improvement at maturity.(3) We defined a cooperative uptake locus when QTLs were detected for more than 2 elements of the N, P and K contents in roots, shoots or total plants (QRnc, QSnc, QTnc, QRpc, QSpc, QTpc, QRkc, QSkc and QTkc). Analogously, a cooperative utilization locus was defined when QTLs were detected for more than 2 elements of the N, P and K utilization efficiencies in roots, shoots or total plants (QRnue, QSnue, QTnue, QRpue, QSpue, QTpue, QRkue, QSkue and QTkue). In this study, a total of 53 CUU loci (L1-L53) were found. Of these, 13 loci (L3, L5, L8, L11, L16, L21, L23, L26, L38, L42, L44, L45 and L51) were related to cooperative uptake only, 21 loci (L10, L12, L13, L18, L28, L31, L32, L33, L35, L36, L37, L39, L40, L41, L43, L47, L48, L49, L50, L52 and L53) were related to cooperative utilization only, and 19 loci were related to cooperative uptake and utilization simultaneously (L1, L2, L4, L6, L7, L9, L14, L15, L17, L19, L20, L22, L24, L25, L27, L29, L30, L34 and L46).(4) Glutamine synthetase (GS) is a key enzyme in the formation of the amino acid glutamine during N assimilation. The characterization of GS genes and the development of functional markers are very important for marker-assisted selection (MAS) in wheat breeding. In the present study, the full-length genomic DNA (gDNA) sequence of TaGS1a was obtained from 60 wheat varieties. TaGS1a comprises 3,415 bp and has eleven exons and ten introns. Nine single nucleotide polymorphisms (SNPs) and two insertions and deletions of DNA segments (InDels) were detected in introns, resulting two haplotypes: Hap 1 and Hap 2. A cleaved amplified polymorphic sequence (CAPS) marker was developed to distinguish the two haplotypes. The CAPS marker was located on chromosome 6D using Chinese Spring nullisomic–tetrasomic lines, and mapped at 2.5 cM from the marker barc1121b in a RIL population. The completely corresponding results between quantitative trait locus (QTL) analysis and association analysis suggested that the TaGS1a gene had functions for the ratio of root and shoot for dry weight and N, P and K contents during seedling stage, and for grain size traits during maturity stage. Four QTLs for seedling traits and seven QTLs for grain traits were detected.