The Phenotypic Analysis And Gene Mapping Of Short Lateral Root Mutant(lrs-1) In Soybean

Root system is an important organ for fixing plants,obtaining water and nutrients,and adapting to stress.Soybean is one of main root system plant,in which lateral roots determine the spatial distributionof root system（root architecture）in growth medium,and have an important influence on the adaptability and yield.Understandying of the lateral roots development of soybean is of great significance for optimizing root architecture,increasing soybean yield and stress resistance.In this study,the important agronomic traits,root morphology and anatomical structure of mutant,lrs-1,were compared with those of wild type.The genetics basis of lrs-1 was identified by genetic analysis using F₂ population deriving from the hybrid between Huaxia3 and lrs-1.Two mixed pools were constructed with individuals of extreme types separated from F₂ population.The mutation gene was mapped in the 10497514～32404202（21.91Mb）region of chromosome 12 using MutMap strategy,and the candidate gene was finally identified as Glyma.12G168900.Bioinformatics analysis of the candidate gene and its homologous gene characteristics were carried out.The main results are as follows:1.The differences in root traits were compared between lrs-1 and wild type.The developmental dynamics of lateral roots of lrs-1 and Huaxia 3 were observed by hydroponic and shallow culture.It was found that the lrs-1 mutation affects the lateral root length from the start of lateral roots until the lateral root development is completed.2.The differences in root anatomical structure were compared between lrs-1 and wild type.By observing the sections of lrs-1 and Huaxia 3,it was found that the cells in the anterior basal part of lateral roots of Huaxia 3 were longer than those of lrs-1,which may be the reason why the lateral roots of Huaxia 3 were longer than those of lrs-1.It was also found that the morphology of lrs-1 xylem cells was a ring,which was different from that of soybean xylem cells in the shape of four petals,but whether the difference of xylem morphology was related to the mutation of lrs-1 gene needs further verification.3.The differences in main agronomic traits were compared between lrs-1 and wild type.The results showed that there was no significant difference in yield between lrs-1 and wild type（Huaxia 3）,but the number of effective branches,nodes and pods of lrs-1 was significantly more than that of Huaxia 3.It was also found that there was no significant difference in petiole development between lrs-1 and Huaxia 3 by scanning the leaves of lrs-1 and Huaxia 3.The results showed that Huaxia 3 and lrs-1 differed not only in lateral root length,but also in branching,segmenting and drum grains.4.The differences of stress resistances were compared between lrs-1 and wild type.The root morphology of lrs-1 and Huaxia 3 under heavy metal and deficiency stress was observed.It was found that lrs-1 and Huaxia 3 had the same response to heavy metal cadmium and lead,but different responses to iron and phosphorus deficiency.The total root length,lateral root length and total root surface area of lrs-1 increased under iron deficiency stress,but the total root length,lateral root length and total root surface area of Huaxia 3decreased under phosphorus deficiency stress.The increase of root length,lateral root length and total root surface area was much greater than that of Huaxia 3,indicating that lrs-1 was more significant response to iron and phosphorus deficiency stress.Through drought stress on lrs-1 and Huaxia 3,root morphology was observed.It was found that under drought stress,Shoot dry weight of lrs-1 decreased less than Huaxia 3,indicating that Huaxia 3 was more sensitive to drought than lrs-1.5.The mutation gene of lrs-1was mapped on chromosome 12（21.91Mb）by MutMap.Genetic analysis showed that short lateral root was a single gene recessive trait.The lrs-1mutation gene was mapped on chromosome 12（21.91Mb）by MutMap.There were 8mutation points,and primers were designed at the mutation points.The agarose gel electrophoresis and polypropylene gel electrophoresis confirmed that the interval was closely related to the lrs-1 mutation gene,and the 32404202 was completely linked to the short lateral root trait.6.Bioinformatics analysis of Glyma.12G168900 and its homologous gene were carred.Glyma.12G168900 encodes a homologous gene of CPSF73-I in Arabidopsis thaliana.The mutation point of the gene was located in Glyma.12G168900 coding region.The deletion of a base A leads to code-shifting mutation and early termination of translation,leading to the deletion of CPSF73-100＿C domain.Glyma.08G188800,a homologous gene in soybean genome,is highly similar to Glyma.12G168900 in protein sequence.The data of soybean expression in public database showed that Glyma.12G168900 expressed much more in soybean roots than Glyma.08G188800.By comparing the promoter regions of Glyma.12G168900 and Glyma.08G188800,it was found that there were significant differences in the types and numbers of promoter elements between the two genes,which might be related to their expression characteristics.Glyma.12G168900 is a homologous gene AT1G61010 in Arabidopsis thaliana.Its protein sequence is highly similar to Glyma.12G168900.