Centromere repositioning and shifts in wheat evolution

The centromere is the region of a chromosome that directs its separation and plays an important role in cell division and reproduction of organisms.Elucidating the dynamics of centromeres is an alternative strategy for exploring the evolution of wheat.Here,we comprehensively analyzed centromeres from the de novoassembled common wheat cultivar Aikang58(AK58),Chinese Spring(CS),and all sequenced diploid and tetraploid ancestors by chromatin immunoprecipitation sequencing,whole-genome bisulfite sequencing,RNA sequencing,assay for transposase-accessible chromatin using sequencing,and comparative genomics.We found that centromere-associated sequences were concentrated during tetraploidization and hexaploidization.Centromeric repeats of wheat(CRWs)have undergone expansion during wheat evolution,with strong interweaving between the A and B subgenomes post tetraploidization.We found that CENH3 prefers to bind with younger CRWs,as directly supported by immunocolocalization on two chromosomes(1A and 2A)of wild emmer wheat with dicentromeric regions,only one of which bound with CENH3.In a comparison of AK58 with CS,obvious centromere repositioning was detected on chromosomes 1B,3D,and 4D.The active centromeres showed a unique combination of lower CG but higher CHH and CHG methylation levels.We also found that centromeric chromatin was more open than pericentromeric chromatin,with higher levels of gene expression but lower gene density.Frequent introgression between tetraploid and hexaploid wheat also had a strong influence on centromere position on the same chromosome.This study also showed that active wheat centromeres were genetically and epigenetically determined.

Changes in Root Hydraulic Conductivity During Wheat Evolution

Abstract: A better understanding of the mechanisms of water uptake by plant roots should be vital for improving drought resistance and water use efficiency (WUE). In the present study, we have demonstrated correlations between root system hydraulic conductivity and root characteristics during evolution using six wheat evolution genotypes (solution culture) with different ploidy chromosome sets (Triticum boeoticum Bioss., T. monococcum L.: 2n=2x=14; T. dicoccides Koern., T. dicoccon (Schrank) Schuebl.: 2n = 4x = 28; T. vulgare Vill., T. aestivum L. cv. Xiaoyan No. 6: 2n = 6x = 42). The experimental results showed that significant correlations were found between root system hydraulic conductivity and root characteristics of the materials with the increase in ploidy chromosomes (2x→6x) during wheat evolution. Hydraulic conductivity of the wheat root system at the whole-plant level was increased with chromosome ploidy during evolution, which was positively correlated with hydraulic conductivity of single roots, whole plant biomass, root average diameter, and root growth (length, area), whereas the root/shoot ratio had an inverse correlation with the hydraulic conductivity of root system with increasing chromosome ploidy during wheat evolution. Therefore, it is concluded that that the water uptake ability of wheat roots was strengthened from wild to modern cultivated species during evolution, which will provide scientific evidence for genetic breeding to improve the WUE of wheat by genetic engineering.

Cloning and Characterization of Genes Coding for Fructan Biosynthesis Enzymes (FBEs) in Triticeae Plants

Fructan is not only a carbon source for storage but also plays an important role as anti-stress agents in many plant species. Complex fructans having both β-（2,1）- and β-（2,6）-linked fructosyl units accumulate in Triticeae plants commonly. Three enzymes （sucrose： sucrose 1-fructosyltransferase, 1-SST, EC： 2.4.1.99; sucrose： fructan 6-fructosyltransferase, 6- SFT, EC： 2.4.1.10; and fructan： fructan 1-fructosyltransferase, 1-FFT, EC： 2.4.1.100） were involved in fructan biosynthesis in Triticeae plant species. We successfully isolated these genes from tetraploid wheat （Triticum turgidum, genotype： AABB）, common wheat （Triticum aestivum L., genotype： AABBDD） and three wild relatives of common wheat, Triticum urartu Thum. （the origin of the AA genome）, Aegilops speltoides （Tausch） Gren. （the putative source of the SS genome） and Aegilops tauschii Coss. （the source of the DD genome）. Sequence analysis revealed that all the FBEs （fructan biosynthetic enzymes） had three highly conserved functional motifs except 1-SST （EU981912） from tetraploid wheat species only with conserved DPNG. Low pI （isoelectric point） and potential N-glycosylation sites were predicted, which were crucial for protein compartmentation and post-translational process. Analysis on subcelluar localization signals showed that only 6-SFT had vacuolar-directed signal. Sequences alignment result showed that 1-SST and 1-FFT were more conservative and had closer relationship each other, while 6-SFT was more active during the evolution processing. According to the syntenic relationship between wheat and rice genome, FBEs were predicated to be located on the homeologous group 6 and group 2 chromosomes. Expression profile confirmed that expression of all the three FBEs were drought-stress induced. This study can assist to establish a useful theoretical platform for cold- or drought-tolerant improvement of wheat by modulating FBEs expression.