State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Sciences, South China Agricultural University, Guangzhou 510642, China.
College of Grassland Science and Technology, China Agricultural University, Beijing 100193, China.
Plant Physiol. 2022 Aug 29;190(1):60-71. doi: 10.1093/plphys/kiac257.
Spikelets are highly specialized and short-lived branches and function as a constitutional unit of the complex grass inflorescences. A series of genetic, genomic, and developmental studies across different clades of the family have called for and permitted a synthesis on the regulation and evolution of spikelets, and hence inflorescence diversity. Here, we have revisited the identity specification of a spikelet, focusing on the diagnostic features of a spikelet from morphological, developmental, and molecular perspectives. Particularly, recent studies on a collection of barley (Hordeum vulgare L.), wheat (Triticum spp.), and rice (Oryza sativa L.) mutants have highlighted a set of transcription factors that are important in the control of spikelet identity and the patterning of floral parts of a spikelet. In addition, we have endeavored to clarify some puzzling issues on the (in)determinacy and modifications of spikelets over the course of evolution. Meanwhile, genomes of two sister taxa of the remaining grass species have again demonstrated the importance of genome duplication and subsequent gene losses on the evolution of spikelets. Accordingly, we argue that changes in the orthologs of spikelet-related genes could be critical for the development and evolution of the spikelet, an evolutionary innovation in the grass family. Likewise, the conceptual discussions on the regulation of a fundamental unit of compound inflorescences could be translated into other organismal groups where compound structures are similarly formed, permitting a comparative perspective on the control of biological complexity.
小穗是高度特化和短命的枝条，作为复杂禾本科花序的组成单位。一系列跨越不同科的遗传、基因组和发育研究呼吁并允许对小穗的调控和进化进行综合研究，从而推动花序多样性的研究。在这里，我们重新审视了小穗的身份特征，重点从形态、发育和分子角度探讨了小穗的诊断特征。特别是，最近对大麦（Hordeum vulgare L.）、小麦（Triticum spp.）和水稻（Oryza sativa L.）突变体的一系列研究强调了一组转录因子在小穗身份控制和小穗花部模式形成中的重要性。此外，我们还努力澄清了在进化过程中小穗的（不）确定性和修饰方面的一些令人困惑的问题。与此同时，两个剩余禾本科姐妹类群的基因组再次证明了基因组加倍和随后基因丢失对小穗进化的重要性。因此，我们认为与小穗相关基因的同源基因的变化可能对小穗的发育和进化至关重要，这是禾本科的一个进化创新。同样，对复合花序基本单位调控的概念性讨论可以转化为其他类似复合结构形成的生物群体，从而可以对生物复杂性的调控进行比较研究。
