Grass flowers: An untapped resource for floral evo‐devo

Abstract

The abrupt origin and rapid diversification of the flowering plants presents what Darwin called "an abominable mystery". Floral diversification was a key factor in the rise of the flowering plants, but the molecular underpinnings of floral diversity remain mysterious. To understand the molecular biology underlying floral morphological evolution, genetic model systems are essential for rigorously testing gene function and gene interactions. Most model plants are eudicots, while in the monocots genetic models are almost entirely restricted to the grass family. Likely because grass flowers are diminutive and specialized for wind pollination, grasses have not been a major focus in floral evo-devo research. However, while grass flowers do not exhibit any of the raucous morphological diversification characteristic of the orchids, there is abundant floral variation in the family. Here, we discuss grass flower diversity, and review what is known about the developmental genetics of this diversity. In particular, we focus on three aspects of grass flower evolution: (1) the evolution of a novel organ identity-the lodicule; (2) lemma awns and their diversity; and (3) the convergent evolution of sexual differentiation. The combination of morphological diversity in the grass family at large and genetic models spread across the family provides a powerful framework for attaining deep understanding of the molecular genetics of floral evolution.

Dominant inhibition of awn development by a putative zinc‐finger transcriptional repressor expressed at the B1 locus in wheat

“…Awns are bristle-like structures extending from the lemma-tipmidvein in the Poaceae grasses including cereal crop species such as wheat (Triticum aestivum and T. durum), barley (Hordeum vulgare) and rice (Oryza sativa). As an extension of the lemma, awns have long been considered modified leaves; however, evidence suggests that the origin or homology of the lemma itself may be as a modified sepal or novel organ type with bract and sepal characteristics (Grundbacher, 1963;Fabien & Hitoshi, 2015;Schrager-Lavelle et al, 2017). In wild species, the main function of awns is grain dispersal by way of hygroscopically propelling the seed dispersal unit on the ground and into the soil (Elbaum et al, 2007).…”

Genetic Loci Underlying Awn Morphology in Barley

“…The awn is a green floral organ extending from the lemma, which itself is a modified sepal in origin [9,10]. Although it is a nonessential organ to the growth and reproduction of the plant, when present, the awn is highly active in photosynthesis and can contribute significantly to the filling of developing grains [11].…”

Evolution, development, and genetics of floral display—form, size, and arrangement

“…Despite its importance to angiosperm diversification, our knowledge of the evolutionary patterns and the underlying developmental and genetic basis of the floral display is still limited. In the modern times, with the advent of integrating approaches among phylogenetics, ecology, molecular genetics, and development, plant biologists have begun to shed lights on the evolutionary patterns, the underlying driving forces, and the developmental and molecular basis of the floral diversity in some angiosperm lineages (e.g., Gerrath et al, ; Kulbaba et al, ; Liu et al, ; Nikolov & Davis, ; Schrager‐Lavelle et al, ; Zhang et al, ; see review by Ma et al, , this issue).…”

“…Most works presented at the symposium were included in this special issue of Journal of Systematics and Evolution . This issue includes both reviews and research papers reporting works on diverse angiosperm lineages, from dicots (Gerrath et al, ; Kulbaba et al, ; Liu et al, ; Nikolov & Davis, ; Zhang et al, ) to monocots (Schrager‐Lavelle et al, ), from autotrophs (Gerrath et al, ; Kulbaba et al, ; Liu et al, ; Schrager‐Lavelle et al, ; Zhang et al, ) to heterotrophs (Nikolov & Davis, ), and from ecological (Kulbaba et al, ) to morphological and molecular aspects (Gerrath et al, ; Liu et al, ; Nikolov & Davis, ; Schrager‐Lavelle et al, ; Zhang et al, ).…”

“…They compared these characteristics on a phylogenetic framework and concluded that each major clade of the Vitales had evolved a unique set of inflorescence morphology, including the homologous tendril characters (also see Zhang et al, ). Schrager‐Lavelle et al () argued that the grass flowers can be an excellent model for studying floral evo‐devo although the natures of the flowers are specialized for wind pollination (see Soreng et al, ). These authors illustrated the many floral variations found in the family and conveyed that grass flowers can also be a powerful tool to understand the molecular genetics of floral evolution.…”