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Summary 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.We discovered that awned lemmas that evolved independently share similarities in developmental trajectory. In addition, in two species with independently derived awns and differing awn morphologies (Brachypodium distachyonandAlopecurus myosuroides), we found that orthologs of theYABBYtranscription factor geneDROOPING LEAFare required for awn initiation. Our analyses of awn development inBrachypodium distachyon,Alopecurus myosuroides, andHolcus lanatusalso revealed that differences in the relative expansion of awned lemma compartments can explain diversity in awn morphology at maturity.Our results show that developmental conservation can underlie replicated evolution and can potentiate the evolution of morphological diversity. 

Synopsis How did plant sexuality come to so hauntingly resemble human sexual formations? How did plant biology come to theorize plant sexuality with binary formulations of male/female, sex/gender, sperm/egg, active males and passive females—all of which resemble western categories of sex, gender, and sexuality? Tracing the extant language of sex and sexuality in plant reproductive biology, we examine the histories of science to explore how plant reproductive biology emerged historically from formations of colonial racial and sexual politics and how evolutionary biology was premised on the imaginations of racialized heterosexual romance. Drawing on key examples, the paper aims to (un)read plant sexuality and sexual anatomy and bodies to imagine new possibilities for plant sex, sexualities, and their relationalities. In short, plant sex and sexuality are not two different objects of inquiry but are intimately related—it is their inter-relation that is the focus of this essay. One of the key impulses from the humanities that we bring to this essay is a careful consideration of how terms and terminologies are related to each other historically and culturally. In anthropomorphizing plants, if plant sexuality were modeled on human sexual formations, might a re-imagination of plant sexuality open new vistas for the biological sciences? While our definitions of plant sexuality will always be informed by contemporary society and culture, interrogating the histories of our theories and terminologies can help us reimagine a biology that allows for new and more accurate understandings of plants, plant biology, and the evolution of reproduction. 

Significance Floral morphology is immensely diverse. One developmental process acting to shape this diversity is growth suppression. For example, grass flowers exhibit extreme diversity in floral sexuality, arising through differential suppression of stamens or carpels. The genes regulating this growth suppression and how they have evolved remain largely unknown. We discovered that two classic developmental genes with ancient roles in controlling vegetative branching were recruited to suppress carpel development in maize. Our results highlight the power of forward genetics to reveal unpredictable genetic interactions and hidden pleiotropy of developmental genes. More broadly, our findings illustrate how ancient gene functions are recruited to new developmental contexts in the evolution of plant form. 

Summary The evolutionary modification of development was fundamental in generating extant plant diversity. Similarly, the modification of development is a path forward to engineering the plants of the future, provided we know enough about what to modify. Understanding how extant diversity was generated will reveal productive pathways forward for modifying development. Here, I discuss four examples of developmental pathways that have been remodeled by changes to protein–protein interactions. These are cases where changes to developmental pathways have been paralleled by recent changes, selected for or engineered by humans. Extant plant diversity represents a vast treasure trove of molecular solutions to ecological problems. Mining this treasure trove will allow for the intentional modification of plant development for solving future problems. 

Crop engineering and de novo domestication using gene editing are new frontiers in agriculture. However, outside of well-studied crops and model systems, prioritizing engineering targets remains challenging. Evolution can guide us, revealing genes with deeply conserved roles that have repeatedly been selected in the evolution of plant form. Homologs of the transcription factor genesGRASSY TILLERS1(GT1) andSIX-ROWED SPIKE1(VRS1) have repeatedly been targets of selection in domestication and evolution, where they repress growth in many developmental contexts. This suggests a conserved role for these genes in regulating growth repression. To test this, we determined the roles ofGT1andVRS1homologs in maize (Zea mays) and the distantly related grass brachypodium (Brachypodium distachyon) using gene editing and mutant analysis. In maize,gt1; vrs1-like1(vrl1) mutants have derepressed growth of floral organs. In addition,gt1; vrl1mutants bore more ears and more branches, indicating broad roles in growth repression. In brachypodium,Bdgt1;Bdvrl1mutants have more branches, spikelets, and flowers than wild-type plants, indicating conserved roles forGT1andVRS1homologs in growth suppression overca.59 My of grass evolution. Importantly, many of these traits influence crop productivity. Notably, maizeGT1can suppress growth in arabidopsis (Arabidopsis thaliana) floral organs, despiteca. 160 My of evolution separating the grasses and arabidopsis. Thus,GT1andVRS1maintain their potency as growth regulators across vast timescales and in distinct developmental contexts. This work highlights the power of evolution to inform gene editing in crop improvement. 

Every spring, something seemingly miraculous happens in the woods in certain parts of the world—thousands of leaves burst from buds on bare tree branches, transforming the landscape from the browns and grays of winter to the bright greens of spring and summer. Although this process is most obvious in regions with drastic seasonal changes, seed plants all over the world regularly produce and lose leaves as they grow. How does this happen? Where do these leaves come from? The cells that make up these leaves are produced by a tiny cluster of cells called the shoot apical meristem. The cells in the shoot apical meristem have the potential to develop into various kinds of cells. Through cell division, meristem cells eventually produce all the above-ground parts of a plant, including leaves. In this article, we explain how meristems function and highlight how these tiny clusters of cells impact our day-to-day lives. We will also provide suggestions for observing meristems at work. 

Grass inflorescence branching involves the integration of competing signals that regulate leaf and meristem growth.