Fig. 4.

INT-M likely contributes to divergence of inflorescence indeterminacy/determinacy in barley and wheat. (A) Unlike Hordeum, most Triticeae species have determinate IMs. Brachypodium distachyon is used as the outgroup. (B) SAM length gradually decreases over development in H. chilense, but sharply declines in several Triticeae species at TM-SM or FM stages (stars) that coincide with the transitions of an IM to a TSM. The exact timing of this transition varies between species, at TM-SM stage in four examined Triticeae species and at FM stage in Einkorn. The reduction in each species is statistically significant (P < 0.05), except in Heteranthelium using the Tukey test over development in each species; however, only one measurement of TM-SM stage is recorded for Heteranthelium (out of a total of 30 measurements for all stages). It should be noted that the meristem length is also reduced in H. chilense as the apical meristem is consumed to produce lateral organs, but the magnitude/rate is relatively lower (a more flattened curve) (SI Appendix, Table S4). Replicate number for each stage of each species is listed in SI Appendix, Table S4. (C) The cultivated tetraploid wheat Kronos harboring mutations in miR172 target site (rAP2L-A5) and two independent MIM172 transgenic lines have prolonged and elevated expression of TtAP2L-A5 (19) and form the wild-type determinate inflorescences. The null mutation ap2l-A5 leads to production of sterile lemmas as int-m mutants. (D–F) AP2L-5 orthologs in selected Triticeae species are localized in IM, SM, and lemma over development. Transcripts of AP2L-5 orthologs in Hordeum species (D and E) persist broadly in IM at FM and/or StP stages, while TmAP2L-A5 (D) and DvAP2L-V5 (F) are more localized in the SAM.