Abstract
The identification of biological mechanisms underlying the development of complex quantitative traits, including those that contribute to plant architecture, yield and quality potential, and seed dispersal, is a major focus in the evolutionary biology and plant breeding. The awn, a bristle-like extension from the lemma in the floret, is one of the distinct morphological and physiological traits in grass species. Awns are taught as an evolutionary trait assisting seed dispersal and germination and increasing photosynthesis. Awn development seems to be complex process, involving dramatic phenotypic and molecular changes. Although recent advances investigated the underlying morphological and molecular genetic factors of awn development, there is little agreement about how these factors interact during awn formation and how this interaction affects variation of awn morphology. Consequently, the developmental sequence of the awn is not yet well understood. Here, we review awn morphological and histological features, awn development pathways, and molecular processes of awn development. We argue that morphological and molecular genetic mechanisms of awn development previously studied in major cereal crops, such as barley, wheat, and rice, offered intriguing insights helping to characterize this process in a comparative approach. Applying such an approach will aid to deeply understand factors involved in awn development in grass species.
Highlights
In monocotyledonous cereal crops, such as rice (Oryza sativa L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and rye (Secale cereale L.), as well as several forage grasses, the inflorescence is characterized by bristle-like extensions, called awns, adhered at the tip end of the lemmas in the florets [1]
Awns are beneficial in wild species because they aid in seed dispersal, as the barbed awns adhere the seed to animal fur [6]
Awn development was described morphologically and genetically, especially in major cereal crops like rice, wheat and barley. These advancements offer an intriguing paradigm for studying the evolution and domestication of grasses, and have significant implications for future breeding programs
Summary
In monocotyledonous cereal crops, such as rice (Oryza sativa L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and rye (Secale cereale L.), as well as several forage grasses, the inflorescence is characterized by bristle-like extensions, called awns, adhered at the tip end of the lemmas in the florets [1]. On the contrary, have a round shape in transverse section with single vascular bundles and a lack of chlorenchyma tissues, implying their minor contribution to photosynthesis [1] Supporting this observation, awn removal experiments revealed a minor impact on grain yield and, rice species with shorter or nonexistent awns were preferred by early cultivators to enhance harvesting and postharvest processing. Despite the undisputable role of awns for inflorescence architecture and their putative impact for yield determination, details regarding how the awn is formed and how its morphology is variable among species remain elusive, and a clear model explaining the awn developmental process is needed As such, it demands solid and basic skills of the major plant developmental processes. Understanding awn development is essential for agriculture, with respect to improving yield and quality traits of grass species
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