Population genomic analysis unravels the evolutionary roadmap of pericarp color in rice

Pigmented rice stands out for its nutritional value and is gaining more and more attention.Wild rice,domes-ticated red rice,and weedy rice all have a red pericarp and a comprehensive genetic background in terms of the red-pericarp phenotype.We performed population genetic analyses using 5104 worldwide rice acces-sions,including 2794 accessions with red or black pericarps,85 of which were newly sequenced in this study.The results suggested an evolutionary trajectory of red landraces originating from wild rice,and the split times of cultivated red and white rice populations were estimated to be within the past 3500 years.Cultivated red rice was found to feralize to weedy rice,and weedy rice could be further re-domesticated to cultivated red rice.A genome-wide association study based on the 2794 accessions with pigmented peri-carps revealed several new candidate genes associated with the red-pericarp trait for further functional characterization.Our results provide genomic evidence for the origin of pigmented rice and a valuable genomic resource for genetic investigation and breeding of pigmented rice.

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.