Genetic Diversity Of Cluster Bean And The Transcriptome Analysis Of Its Developing Seeds

Guar bean(Cyamopsis tetragonoloba L.Taub),a spiecy native to Africa,is an excellent tropical and subtropical legume crop.It is drought tolerant and it can improve soil fertility.Guar gum extracted from guar bean can be used in oil and natural gas exploitation.Its modified products are also widely used in food,medicine,papermaking,textile,daily cosmetics and other industries.At present,the research information on guar bean is not systematic.In this paper,the genetic diversity of 257 guar bean germplasm resources was studied,which is fundamental for the improvement of guar bean varieties in the future.And the content of several sugars as well as the enzyme activities responsible for their formation and catabolism was monitored during the guar seed development in the three key stages.Furthermore,RNAseq analysis was performed on guar bean seeds 30 and 40 days after flowering(DAF),and potential genes related to guar gum biosynthesis were identified.The main results are as follows:1.Statistical analysis of 10 phenotypic traits of 257 guar bean germplasm from different sources showed that the genetic variations of each phenotypic trait were different.Among them,the genetic variation coefficient between the initial flowering period and the initial ripening period ranged from 2.41%to 5.58%,the variation was relatively small;the variation coefficient of seedling stage,pod height,plant height,effective node number of main stem and grain weight of single plant ranged from 20.20%to 45.75%;the variation coefficient of effective branching was the largest,amounting to 375.76%.According to the phenotypic traits,257 materials can be divided into 4 groups:Group ? contains 14 accessions,and the plant height in this group is the smallest among all tested accessions,the single plant grain weight is low,and the number of main stem nodes is less.Group ? only include 2 accessions,this group was featured with high plant height,both are more than 2 m;Group ?including 7 accessions,this subset characterized for its effective branch number,number of main stem section and the high yield;Group IV included 234 acessions,the group includes maximum number with no obvious characteristics.2.Eighteen pairs of SSR primers were selected to analyze 257 guar bean accessions,and a total of 71 alleles were detected.The average alleles of each site were 3.94 and the variation ranged from 2 to 7.According to the diversity index analysis,the Simpson index is 0.2757-0.7904,with an average value of 0.5632.The Shannon-Weiner index ranges from 0.4027 to 1.1475 with an average of 0.8376.The results indicated that the collected guar bean showed high genetic diversity and abundant gene types.UPGMA cluster analysis showed that 257 accessions can be divided into four groups,e.g.?,?,? and ?.Category I included 94 accessions,this group have no obvious phenotypic traits,and they are mainly coming from India.Category II include 76 accessions,with wireless podding habits,high plant height,and low height of podding branch as well as effective branch and main stem.These accessions are mainly from Pakistan.Category ? has 45 accessions,and characterized by its high podding height,abudant branch number,more grain weight per plant,most component in this group are from the United States.Category IV include 42 accessions,with the low plant height and low grain weight per plant,the majority of this group is collected in China.3.During the whole process of seed development,the sucrose content increased,fructose and glucose content decreased,while total soluble sugar showed no remarkable change.Inv and SS decomposition activity gradually decreased,SS synthesis activity did not change significantly,while SPS activity decreased gradually.The above results indicate that seed sugar metabolism,especially glucose metabolism closely linked with biosynthesis of guar gum.4.Guar bean seeds collected from 30 and 40 days after flowering(DAF)were used for RNA-seq analysis in this study.A total of 2,535 and 2,724 preferentially expressed genes were found in 30 and 40 DAF endosperm,and 3,720 and 2,530 preferentially expressed genes were found in 30 and 40 DAF DAF embryo.Among which,mannan synthase genes,a-galactosyltransferase genes and cellulose synthase genes were specifically expressed in 30 and 40DAF endosperm.Since the main component of guar gum is galactomannan,the high expression of glycometabolism in endosperm is consistent to the expectation.On the other hand,seed store protein and fatty acid synthesis protein related genes were also highly expressed in 30 and 40 DAF embryo.Overall,many potential genes related guar gum synthesis were found in this study,which will be helpful for further gene function identification involving in guar gum biosynthesis.