QTL Mapping And Proteomics Analysis For Seminal Root Length Of Wheat Seedling Under Control And Low Nitrogen Conditions

Root system is a vital plant organ owing to its involvement in water absorption and nutrient acquisition.It is of great significance to analyze the molecular basis of plant root growth and development for the genetic improvement of crop root traits,thereby increasing nutrient use efficiency.Wheat is one of the important food crops,there are only a few genetic loci available for genetic improvement of wheat root traits in breeding,and the molecular regulatory pathways for root growth and development are still unclear at present.Low nitrogen?LN?is known to promote wheat root growth,but little is known about the mechanism.This study used a set of “XY54×J411” recombinant inbred lines?RIL?as materials.Firstly,QTLs for maximum root length?MRL?and seminal root elongation?SRE?of wheat roots were mapped under control and LN conditions.Then typical long root and short root lines from the RIL population were selected to explore differentially abundant proteins and regulatory pathways regulating wheat root growth by comparative proteomics;At the same time,lines exhibiting significantly enhanced seminal root growth under LN conditions and other lines exhibiting no obvious induction of seminal root growth by LN stress from the RIL population were selected to explore the molecular mechanism of low nitrogen-promoted wheat root growth by comparative proteomics.The main findings obtained are as follows:1.The MRL of XY54 was significantly longer than that of J411 under both CK and low nitrogen conditions.The root growth of XY54 was promoted significantly by LN,but that of J411 was not obvious.The root length of different RIL lines and their response to low nitrogen also showed large genetic variations.We totally detected 32 QTLs for MRL and SRE which located at 12 loci and distributed on 7 chromosomes under control and LN conditions.Among them,16 QTLs were mapped under CK,including 13 QTLs for MRL and 3 QTLs for SRE.The percentage of phenotypic variation explained by individual MRL QTL varied from 4.7% to 53.2%,while the percentage of phenotypic variation explained by individual SRE QTL was between 9.7% and 26.3%.Sixteen QTLs were mapped under LN conditions,including 13 QTLs for MRL and 3 QTLs for SRE.The percentage of phenotypic variation explained by individual MRL QTL ranged from 5.8% to 59.2%,while the percentage of phenotypic variation explained by individual SRE QTL was between 5.2% and 23.6%.We also found that most QTLs are clustered and only a few QTL exist alone.2.From the "XY54×J411" RIL population,15 lines with the longest root length and another 15 lines with the shortest root length were selected as the LRM group and the SRM group,respectively.Using LRM group,SRM group,XY54 and J411 as materials,80 differentially abundant proteins?DAPs?involved in the regulation of wheat seminal root length were obtained by comparative proteomics method.Among the DAPs that are significantly up-regulated in the long root genotypes,9 pathways were significantly enriched.These include plant steroid biosynthesis pathway,phenylpropanoid biosynthesis pathway,fatty acid biosynthesis and metabolic pathway and phenylalanine metabolic pathway.The accumulation of CYP51 and DWF1,two key protein in plant steroid biosynthesis pathway,was significantly higher in the long root varieties XY54 and LRM than in the short root varieties J411 and SRM,indicating that the BR biosynthesis pathway was enhanced in the long root genotypes.There are 9 peroxidases belonging to class III peroxidases,of which 6 have increased abundance and the other 3 have decreased abundance in the long root genotypes.It is speculated that in the long root cultivar XY54 and the LRM lines,BR is increased due to the enhancement of BR biosynthesis pathway,and through peroxidases or Ca²⁺ signal or MAPK pathway,BR modulates the production and accumulation of ROS in root tips.This results in a more active apical meristem that allows XY54 and LRM lines to have higher root growth rates and longer seminal root lengths.3.From the "XY54×J411" RIL population,15 lines exhibiting significantly enhanced seminal root growth under LN conditions and another 15 lines exhibiting no obvious induction of seminal root growth by LN stress were defined as LRG group and SRG group,respectively.Using the LRG group,the SRG group and their biparents as materials,84 DAPs were obtained by comparative proteomics which involved in LN-promoted seminal root growth.Pathway enrichment analysis indicated that a series of pathways involved in LN-promoted seminal root growth.Among them,glutathione metabolism,endocytosis,lipid metabolism and phenylpropanoid biosynthesis pathway may play a key role in the regulation of LN-promoted seminal root growth.Some DAPs?such as PLD,glutathione transferase,etc.?involved in these pathways may have high value in the genetic improvement of wheat root traits and nitrogen use efficiency.4.The linkage analysis of the DAPs encoding genes and the mapped QTLs for wheat seminal root length showed that there were 9 QTLs co-localized or tightly linked with DAPs encoding genes.The result indicates that there is a close internal relationship between the QTLs and the DAPs.The DAPs co-localized with QTLs may play a more critical role in regulating wheat root growth.In summary,this study mapped QTLs for wheat MRL and SRE under control and LN conditions,and identified some DAPs and regulatory pathways regulating the growth of wheat seminal roots under control and LN conditions.The results can provide genetic loci and screening markers for the genetic improvement of root traits and nitrogen use efficiency in wheat.