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ARS Home » Pacific West Area » Corvallis, Oregon » Forage Seed and Cereal Research Unit » Research » Publications at this Location » Publication #416091
Research Project: Development of Plant and Molecular Resources to Improve Performance, Utility, and Tolerance of Cool Season Grasses and Legumes

Location: Forage Seed and Cereal Research Unit

Title: Deep homology and developmental constraint underlies the replicated evolution of grass awns

Author
item PATTERSON, ERIN - University Of Massachusetts
item MACGREGOR, DANA - Rothamsted Research
item HEENEY, MICHELLE - University Of Massachusetts
item Gallagher, Joseph
item O'CONNOR, DEVIN - Cambridge University
item NUESSLEIN, BENEDIKT - University Of Massachusetts
item BARTLETT, MADELAINE - University Of Massachusetts

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2024
Publication Date: 10/18/2024
Citation: Patterson, E.L., MacGregor, D., Heeney, M., Gallagher, J.P., O'Connor, D., Nuesslein, B., Bartlett, M. 2024. Deep homology and developmental constraint underlies the replicated evolution of grass awns. New Phytologist. 245(2):835-848. https://doi.org/10.1111/nph.20268.
DOI: https://doi.org/10.1111/nph.20268

Interpretive Summary: Awns are extensions of the lemma, the leaf-like structure that surrounds the rest of the grass flower. These structures have appeared repeatedly in the grass family and have a variety of forms and functions. Here, we asked if awns evolve repeatedly in the grass family due to the same underlying developmental program. Looking across a variety of grass species with independently evolved awns, we found that awns share a similar anatomy and pattern of development. When comparing diverse awn morphologies, these differences could be explained by our understanding of the leaf parts from which lemmas and awns evolved. Additionally, in two distinct grass species with independently evolved awns, the YABBY transcription factor DROOPING LEAF was necessary for awn development, demonstrating a shared genetic program. This work shows how structures like the awn can evolve repeatedly and take on diverse forms through use of the same developmental program.

Technical Abstract: Replicated trait evolution can provide insights into the mechanisms underlying the evolution of biodiversity. One example of replicated evolution is the awn, an organ elaboration in grass inflorescences. Awns are likely homologous to leaf blades. We hypothesized that awns have evolved repeatedly because a conserved leaf blade developmental program is continuously activated and suppressed over the course of evolution, leading to the repeated emergence and loss of awns. To evaluate predictions arising from our hypothesis, we used ancestral state estimations, comparative genetics, anatomy, and morphology to trace awn evolution. In line with our predictions, we discovered that awned lemmas that evolved independently share similarities in anatomy and developmental trajectory. In addition, in two species with independently derived awns and differing awn morphologies (Brachypodium distachyon and Alopecurus myosuroides), we found that the YABBY-family transcription factor gene DROOPING LEAF is required for awn initiation. Despite shared origins, awns often vary in form and function. Our analyses of awn development in Brachypodium distachyon, Alopecurus myosuroides, and Holcus lanatus revealed that differences in leaf compartment development can explain diversity in morphology at maturity. Our results show that developmental conservation can underlie replicated evolution, and can potentiate the evolution of morphological diversity.