Studies On Phylogeny Of Wisteria And The Mechanism Of Lineage Divergence In W.sinensis

The subtropical China is one of the biodiversity hotspots in the world.It has long been considered as both a‘museum’and a‘cradle’for many plants.However,how historical climate oscillation and complex landscape features drive the formation of plant diversity in this region remains largely unknown.More studies based on integration of phylogeny,phylogeography and landscape genetics will provide new insights into the mechanism of plant diversity formation in this region.Wisteria sinensis（Sims）DC.,belonging to the genus Wisteria Nutt.of Fabaceae,is a common deciduous vine in subtropical China.This species mainly distributed in Yellow River valley and Yangtze River valley,and shows significant phenotypic variations in different local populations.In this study,we solved the phylogenetic relationships and evolution of Wisteria,then explored population genetic structure,demographic history and the driving factors of genetic and phenotypic differentiation in W.sinensis.The main results and conclusions are listed as follows:（1）Phylogenetic relationships and historical biogeography of Wisteria based on plastome dataPhylogenetic inferring based on plastome data suggested that the clade of Glycyrrhiza-Wisteriopsis-Wisteria formed sister relationship with the clade composed of other IRLC species.All four species of Wisteria were monophyletic groups.Among them,three East Asian wisterias（W.sinensis,W.floribunda and W.brachybotrys）and W.frutescens formed reciprocal clades,while W.floribunda and W.sinensis were sister to each other.Results of biogeographic analyses and fossil evidences revealed that Wisteria originated in Japan at the Oligocene/Miocene boundary（23.85 Ma,95%HPD:23.26–24.86 Ma）,then spread to North America in Late Miocene（8.66 Ma,95%HPD:2.40–17.38 Ma）.The divergence times within East Asian wisterias were dated in the Early Pleistocene（0.87–2.22 Ma）.In brief,these results suggested that geological changes and climatic oscillation since Late Miocene played important roles in the speciation of Wisteria.（2）Genetic diversity,genetic structure and the divergence time of W.sinensis based on cp DNA sequencesGenetic variation analyses by three cp DNA sequences（rps12-trn V、ycf2 and ycf3-psa A）have identified 27 chloroplast haplotypes in 36 W.sinensis populations.These haplotypes can be divided into two lineages（East lineage vs.West lineage）.The genetic differentiation in West lineage(F_ST=0.613)was higher than that in East lineage(F_ST=0.013).Genetic diversity of two lineages gradually decreased from south to north,which revealed that Wenzhou,Tianmu Mountain and Yellow Mountain were served as refuges of East lineage,while Wuyi Mountain and Hengshan Mountain were refuges of West lineage.BEAST analysis based on a second correction point suggested that the lineage divergence within W.sinensis occurred at 0.64 Ma（95%HPD:0.29–0.95 Ma）,while the onset of the diversification of West/East lineages were dated at 0.27 Ma（95%HPD:0.08–0.58 Ma）and 0.24 Ma（95%HPD:0.04–0.56 Ma）,respectively.（3）Population genetic diversity,genetic structure and demographic history of W.sinensis based on RAD-seq dataThe result of genetic structure analyses based on RAD-seq data also supported the division of East/West lineages within W.sinensis.However,the existence of gene flow between two lineages led to genetic admixtures within them.Genetic diversity of SNPs decreased from south to north in West lineage,and the Tajima’s D value was significantly negative（D=-1.642,0.01<p<0.05）.These results suggested that the West lineage may experience population expansion.Demographic history simulation in FASTSIMCOAL2 revealed that W.sinensis diverged at 0.81 Ma（95%HPD:0.46–1.64 Ma）,which was consistent with the result estimated by cp DNA,and supported the hypothesis that Mid-Pleistocene Transition influenced the lineage divergence of W.sinensis.Subsequently,the West lineage experienced population expansion at 0.26 Ma（95%HPD:0.09–0.78 Ma）,whereas the population size of East lineage remained stable.There was bidirectional and asymmetric gene flow after the divergence between East/West lineages,and the gene flow from the East to the West was higher than that in opposite direction.Therefore,both the lineage divergence of W.sinensis and the population expansion of West lineage were influenced by climate oscillations in Pleistocene.（4）Driving factors of genetic and phenotypic variationsA total of 185 outliers were identified by BAYESCAN and ARLEQUIN,of which one outlier was significantly associated with Precipitation Seasonality（Bio 15）by multiple linear regression analysis.The results of IBD and IBE analyses showed that climate and geographical factors totally explained 32.20%of population genetic variations in W.sinensis.The gradient forest simulation indicated that Precipitation of Coldest Quarter（Bio 19）and Mean Diurnal Range（Bio 2）had the greatest influences on the spatial distribution pattern of genetic variation.Comparative analysis of four phenotypic traits revealed significant phenotypic differences between East/West lineages.West lineage has smaller value of SLA,but larger values of inflorescence length,flower number and leaf hair than East lineage.The P_ST of four traits（0.891–0.963）were significantly higher than the F_ST（0.157）.We found that Bio 2 and Bio 19were also the two most influential climate factors on phenotypic variations by correlation analysis.Thus,geographic isolation,environmental heterogeneity,and natural selection together drive the local adaptation of W.sinensis.This study will improve our understanding of the formation mechanism of biodiversity in subtropical China,and provide abundant supports for the conservation and utilization of Wisteria.