3.2 | Whole-genome duplication, phylogenetic evolution,
and genome synteny
To clarify whole-genome duplication in Pse. libanotica ,
synonymous substitutions (Ks) were calculated in Pse. libanotica ,D. glomerat , and B. distachyon . The peak Ks at 0.20 which
occurred after the divergence peak at 0.05 between Pse.
libanotica and D. glomerat and 0.05 between Pse.
libanotica and B. distachyon (Figure 2B), indicating a
whole-genome duplication event occurred in the common ancestor of
Poaceae. To explore the phylogeny and divergence of the St genome, a
unique set of gene families was identified in 14 Poaceae plants based on
available genomic resources (Figure 2A). Sorghum bicolor andZea mays were C4 plants and diverged firstly in the phylogenetic
tree, followed by Oryza sativa , Brachypodium distachyon,and Dactylis glomerat . Triticeae species were clustered into one
monophyletic group (A. tauschii , H. vulgare , S.
cereale , T. aestivum , T. durum , T. dicoccoides ,T. urartu ). The Pse. libanotica diverged
~10.7 million years ago (Mya) after H. vulgare(~11.9 Mya), the S. cereale and the genusTriticum separated ~9.6 Mya.
Orthologous gene in Pse. libanotica , T. aestivum , T.
urartu , H. vulgare , and D. glomerat were analyzed to
illustrate chromosome collinearity and derivation (Figure S4).Pse. libanotica exhibited conserved chromosome homoeologous
collinearity with A genome, B-subgenome, D-subgenome and H genome, and
varied with D. glomerat. Interestingly, the 4St in Pse.
libanotica and the 4A chromosome of T. urartu displayed highly
consistency, nevertheless, a pericentric inversion was observed in the
4A chromosome, and a 4AL (long arm)-5AL-7BS (short arm) translocation in
the common wheat. However, the St genome and the D. glomeratdisplayed chaotic chromosome collinearity. The 2St and 3St chromosomes
mainly matched to the 1 and 5 chromosomes of D. glomerat , the 5St
had syntenic to the 3 and 4 chromosomes of D. glomerat , and the 7
St was syntenic to the 3 and 7 chromosome groups of D. glomerat(Figure S4). Thus, gene order and location varied among Poaceae
species after divergence, conserved among diploid Triticeae species, and
partly rearranged during polyploidization of Triticeae.