Population genomic analysis reveals domestication of cultivated rye from weedy rye

Rye(Secale cereale)is an important crop with multiple uses and a valuable genetic resource for wheat breeding.However,due to its complex genome and outcrossing nature,the origin of cultivated rye remains elusive.The geneticist N.I.Vavilov proposed that cultivated rye had been domesticated from weedy rye,rather than directly from wild species like other crops.Unraveling the domestication history of rye will extend our understanding of crop evolution and upend our inherent understanding of agricultural weeds.To this end,in this study we generated the 8.5 Tb of whole-genome resequencing data from 116 worldwide accessions of wild,weedy,and cultivated rye,and demonstrated that cultivated rye was domesticated directly from weedy relatives with a similar but enhanced genomic selection by humans.We found that a repertoire of genes that experienced artificial selection is associated with important agronomic traits,including shattering,grain yield,and disease resistance.Furthermore,we identified a composite introgression in cultivated rye from the wild perennial Secale strictum and detected a 2-Mb introgressed fragment containing a candidate ammonium transporter gene with potential effect on the grain yield and plant growth of rye.Taken together,our findings unravel the domestication history of cultivated rye,suggest that interspecific introgression serves as one of the likely causes of obscure species taxonomy of the genus Secale,and provide an important resource for future rye and wheat breeding.

The Genomes of the Allohexaploid Echinochloa crus-galli and Its Progenitors Provide Insights into Polyploidization-Driven Adaptation

The hexaploid species Echinochloa crus-galli is one of the most detrimental weeds in crop fields,especially in rice paddies.Its evolutionary history is similar to that of bread wheat,arising through polyploidization after hybridization between a tetraploid and a diploid species.In this study,we generated and analyzed high-quality genome sequences of diploid(E.haploclada),tetraploid(E.oryzicola),and hexaploid(E.crus-galli)Echinochloa species.Gene family analysis showed a significant loss of disease-resistance genes such as those encoding NB-ARC domain-containing proteins during Echinochloa polyploidization,contrary to their significant expansionduring wheat polyploidization,suggesting that natural selection might favor reduced investment in resistance in this weed to maximize its growth and reproduction.In contrast to the asymmetric patterns of genome evolution observed in wheat and other crops,no significant differences in selection pressure were detected between the subgenomes in E.oryzicola and E.crus-galli.In addition,distinctive differences in subgenome transcriptome dynamics during hexaploidization were observed between E.crus-galli and bread wheat.Collectively,our study documents genomic mechanisms underlying the adaptation of a major agricultural weed during polyploidization.The genomic and transcriptomic resources of three Echinochloa species and new insights into the polyploidization-driven adaptive evolution would be useful for future breeding cereal crops.

Orphan Crops and their Wild Relatives in the Genomic Era

More than half of the calories consumed by humans are provided by three major cereal crops(rice,maize,and wheat).Orphan crops are usually well adapted to low-input agricultural conditions,and they not only play vital roles in local areas but can also contribute to food and nutritional needs worldwide.Interestingly,many wild relatives of orphan crops are important weeds of major crops.Although orphan crops and their wild relatives have received little attentions from researchers for many years,genomic studies have recently been performed on these plants.Here,we provide an overview of genomic studies on orphan crops,with a focus on orphan cereals and their wild relatives.The genomes of at least 12 orphan cereals and/or their wild relatives have been sequenced.In addition to genomic benefits for orphan crop breeding,we discuss the potential ways for mutual utilization of genomic data from major crops,orphan crops,and their wild relatives(including weeds)and provide perspectives on genetic improvement of both orphan and major crops(including de novo domestication of orphan crops)in the coming genomic era.

Horizontal transfer and evolution of the biosynthetic gene cluster for benzoxazinoids in plants

Benzoxazinoids are a class of protective and allelopathic plant secondary metabolites that have been identified in multiple grass species and are encoded by the Bx biosynthetic gene cluster(BGC)in maize.Data mining of 41 high-quality grass genomes identified complete Bx clusters(containing genes Bx1–Bx5 and Bx8)in three genera(Zea,Echinochloa,and Dichanthelium)of Panicoideae and partial clusters in Triticeae.The Bx cluster probably originated from gene duplication and chromosomal translocation of native homologs of Bx genes.An ancient Bx cluster that included additional Bx genes(e.g.,Bx6)is presumed to have been present in ancestral Panicoideae.The ancient Bx cluster was putatively gained by the Triticeae ancestor via horizontal transfer(HT)from the ancestral Panicoideae and later separated into multiple segments on different chromosomes.Bx6 appears to have been under less constrained selection compared with the Bx cluster during the evolution of Panicoideae,as evidenced by the fact that it was translocated away from the Bx cluster in Zea mays,moved to other chromosomes in Echinochloa,and even lost in Dichanthelium.Further investigations indicate that purifying selection and polyploidization have shaped the evolutionary trajectory of Bx clusters in the grass family.This study provides the first candidate case of HT of a BGC between plants and sheds new light on the evolution of BGCs.

PlantcircBase 7.0:Full-length transcripts and conservation of plant circRNAs

Circular RNA(circRNA)is a special type of non-coding RNA that participates in diverse biological processes in both animals and plants.Five years ago,we developed a comprehensive plant circRNA database(PlantcircBase),which has attracted much attention from the plant circRNA community.Here,we report an updated PlantcircBase(v.7.0),which contains 171,118 circRNAs from 21 plant species.Over 31,000 of the circRNAs have full-length sequences constructed based on analysis of 749 bulk RNA sequencing(RNAseq)datasets downloaded from the public domain and Nanopore long-read sequencing results of rice RNAs newly generated in this study.A plant multiple conservation score(PMCS),based on the conservation of both sequence and expression profiles,was calculated for each circRNA to quantify and compare the conservation of all circRNAs.A new parameter,plant circRNA confidence level(PCCL),is introduced to measure the identity reliability of each circRNA based on experimental validation results and the number of references that support the circRNA.All this information and other details of circRNAs can be browsed,searched,and downloaded from PlantcircBase 7.0,which also provides online bioinformatics tools for visualization and sequence alignment.PlantcircBase 7.0 is publicly and freely accessible at http://ibi.zju.edu.cn/plantcircbase/.