Biosystematics and evolutionary relationships of perennial Triticeae species revealed by genomic analyses

Abstract Understanding the classification and biosystematics of species in Triticeae Dumort., an economically important tribe in the grass family (Poaceae), is not an easy task, particularly for some perennial species. Does genomic analysis facilitate the understanding of evolutionary relationships of these Triticeae species? We reviewed literature published after 1984 to address questions concerning: (1) genome relationships among the monogenomic diploid species; (2) progenitors of the unknownYgenome inElymuspolyploids,Xgenome inThinopyrum intermedium, andXmgenome inLeymus; and (3) genome constitutions of some perennial Triticeae species that were unknown or misidentified. A majority of publications have substantiated the close affinity of theEbandEegenomes inTh. bessarabicumandTh. elongatum, supporting the use of a common basic genome symbol. TheEgenome is close to theStgenome ofPseudoroegneriaandABDgenomes ofTriticum/Aegilopscomplex, providing an explanation for transferring genes from theEtoABDgenomes with relative ease. Although the solid proof is still lacking, theW,P, and especiallyXpgenomes are possible origins for theYgenome of polyploidElymus. The absence of theEgenome and the allopolyploidy nature of tetraploidLeymusspecies have been unequivocally confirmed by both cytogenetic and molecular studies. However, the donor of theXmgenomes ofLeymuswas only speculated to be related to thePgenome ofAgropyronandFgenome ofEremopyrum. Intermediate wheatgrass (Th. intermedium) has been extensively studied. The presence of theSt(as the previously designatedX) genome inTh. intermediumis now unequivocal. Its two more closely relatedE1andE2genomes are shown to be older versions of theEgenome rather than the currentEbandEegenomes. Speciation ofTh. intermediumwas similar to that ofTriticum aestivum, in which theJs/Es(likeB) genomes had the greatest differentiation from the currentJ(Eb) genome owning to repetitive sequences of theVgenome, whereas itsSt(likeD) had the least differentiation from the currentStgenome. Species with unknown or misidentified genomes have been correctly designated, including those with theESt,StP,StPY,StWY,EStP,HW,StYHW, andNsXmgenomes. Some of those species have been transferred to and renamed in appropriate genera.