QTL Mapping For Phosphorus Efficiency And Photosynthetic-related Traits In Soybean

Soybeans[Glycine max?L.?Merrill]is one of the most important food and oil crops,accounting for about 56%of the global oilseed seed production.The accumulation of soybean production requires photosynthesis,but photosynthesis depends on phosphorus.Compared with non-leguminous plants,relatively large amounts of phosphorus are required during the growth of the soybean,especially during the pod period.Low-phosphorus stress affects soybean growth in many ways,such as reducing soybean nodule development and nitrogen fixation,increasing flower/pod shedding,and damaging plant whole growth and development,thereby affecting yield and seed quality.Therefore,low-phosphorus stress is considered to be an important limiting factor in limiting soybean production and is also more severe than other nutritional deficiencies,toxins or diseases in soybeans.The cultivation of phosphorus efficient and high light efficiency soybean varieties is an effective way to improve soybean tolerance to low phosphorus and photosynthetic capacity.QTL mapping is used to study the genetic relationship between phosphorus efficiency and photosynthetic traits,and it is also a prerequisite for molecular marker assisted selection breeding.In this study,seven high-density and high-density genetic maps of soybean were constructed from 146 recombinant inbred lines F_8:12 derived from Bogao×Nannong94-156,and QTLs for seven phosphorus efficiency and five photosynthetic traits were carried out at different phosphorus levels the relationship between soybean phosphorus efficiency and photosynthetic traits was analyzed by linkage analysis,phenotypic correlation and QTL co-location.At the same time,two super-progeny families B18 and B20 were screened out from the 146 pedigree materials,and the water culture experiments were carried out under different phosphorus treatments.Through a series of phenotypic identification,including seven phosphorus-related traits,Photosynthetic related traits,four fluorescence parameters,three enzyme activities and ultrastructure of chloroplast were used to study the photosynthetic response mechanism of soybean under low phosphorus stress.The main results of this experiment are summarized as follows:?1?The contents of chlorophyll content,net photosynthetic rate?Pn?,stomatal conductance?Co?and transpiration rate?Tr?of two super-parent materials were decreased under the condition of low phosphorus stress,but B18?phosphorus Efficiency-sensitive materials?were significantly higher than those of B20?low-phosphorus-resistant materials?.In contrast,the intercellular carbon dioxide concentration?Ci?of the two leaves increased?P18 and B20 increased by 36.6%and14.4%,respectively?under low phosphorus stress.For the chlorophyll fluorescence parameters,the maximum photochemical quantum yield?Fv/Fm?,the actual photon quantum yield??PS??and the photochemical quenching coefficient?q^p?of the PS?in the two super-parent materials were decreased,while the non-photochemical quenching coefficient?NPQ?,except for?PS?in B20,the change of other related traits under low phosphorus stress was significant or extremely significant,and the change range was more in B18.These results indicate that the effect of low phosphorus stress on the photosynthetic capacity of phosphorus-sensitive materials is greater.In addition,we found that the activity of 1,5-diphosphate ribavirin?Rubsico?decreased significantly in the B18 material and increased significantly in the low-phosphorus-resistant material B20 under low-phosphorus stress;acid phosphatase?APA?Activity increased in both materials,but the resistance of low-phosphorus-resistant material B20 increased more than that of normal phosphorus concentration,while that of low-phosphorus sensitive material B18 was not significant.Therefore,we further speculate that the photosynthetic capacity of B20 material is less affected by low phosphorus stress,probably because of its significant increase in plant activity to increase plant phosphorus absorption and utilization efficiency,and ultimately to maintain a more stable photosynthetic capacity.?2?P efficiency is an important complex quantitative trait involving multiple genes,and the mechanisms underlying soybean P efficiency are largely unknown.Here,we reported the construction of a high-density genetic map using a specific-locus amplified fragment sequencing?SLAF-seq?strategy in soybean.This map,spanning 3020.59 cM in length,contained 6159 markers on 20 chromosomes,with an average distance of 0.49 cM between adjacent markers.Based on this map,20loci,including eight novel loci,associated with P efficiency-related traits were identified across multiple years and treatments.The confidence intervals of almost all QTLs were refined significantly,and the accuracy of this map was evidenced by coincident detections of the previously identified P efficiency-related genes GmACP1and GmPT1.Notably,a highly significant novel QTL located on chromosome 4,q4-2,was identified across traits,years and treatments.Several candidate genes,such as a pectin methylesterase-encoding gene?Glyma.04G214000?and a protein kinase gene?Glyma.13G161900?,with significantly differential expression upon low-P stress were considered as promising candidates involved in regulating soybean P efficiency.Markers that tightly associated with P efficiency could be used for marker-assisted selection in a soybean P efficient breeding program.Further,dissection of these QTLs will facilitate gene cloning underlying P efficiency in soybean,and increase our understanding of efficient use of P in enhancing crop yield.?3?In this study,we used a combined analysis of phenotypic correlation,linkage mapping,and expression analysis to dissect the relationship between PE and photosynthesis.We found significant phenotypic correlations between PE and photosynthetic related traits,particularly under low P stress.A total of 172 QTLs for both traits were detected and classified into 29 genomic regions.12?41.4%?of 29regions were detected to be associated with both PE and photosynthetic related traits.Three major QTLs,q14-2,q15-2,and q19-2,were found to be associated with both traits and explained 6.6–58.9%of phenotypic variation.A photosynthetic-specific QTL cluster,q12-1,was detected under both normal and low P conditions,suggesting that genes responsible for this region were less effected by low P stress,and could be used in high photosynthetic efficiency breeding programs.In addition,several candidate genes with significantly differential expression upon low P stress,such as a purple acid phosphatase gene?Glyma.19G193900?within q19-2 region,were considered as promising candidates involved in regulating both soybean PE and photosynthetic capacity.Our results reveal a significant genetic relationship between PE and photosynthetic traits,and uncover several major genomic regions specific or common to these traits.