Axillary meristems (AMs) contribute to the growth of a plant, determining adult architecture and reproductive success in response to environmental stimuli. The missing flowers (mf) mutant of sunflower (Helianthus annuus) is defective in AM development. mf lacks shoot branching and ray flowers, occasionally producing few disk flowers. Here we demonstrated that a point mutation in the REGULATOR OF AXILLARY MERISTEM FORMATION‐LIKE (Ha‐ROXL) gene of mf generates a premature stop codon and therefore a nonfunctional bHLH transcription factor, no longer localized in the nucleus, where it should exert its function. Virus‐induced gene silencing of Ha‐ROXL also causes defects in disk and ray flower development. Ha‐ROXL mRNA accumulates at the adaxial boundaries of leaves and AMs. During inflorescence development, Ha‐ROXL is expressed in small arcs of cells before a clear separation between abaxial bracts and disk flower primordia. No Ha‐ROXL mRNA accumulates in mf inflorescences. Several genes known to play roles in plant architecture, auxin transport, and flower development are differentially expressed in mf and Ha‐ROXL‐silenced plants. These results highlight the predominant role of Ha‐ROXL in regulating AMs in sunflower. In dicot, mf is the first mutant for which the ROXL gene is also required for initiation of flower meristems.

中文翻译：

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Ha-ROXL基因是启动向日葵腋生和花分生组织所必需的。

腋生分生组织（AMs）有助于植物的生长，决定成年结构和对环境刺激的繁殖成功。向日葵（Helianthus annuus）的缺失花（mf）突变体在AM发育中存在缺陷。MF缺少枝条和射线花，偶而很少产生圆盘花。在这里，我们证明了在一个点突变腋生分生组织的形成，像稳压器（哈ROXL）的基因MF产生提前终止密码子，因此无功能的bHLH转录因子，在细胞核中，它应该发挥其功能不再本地化。病毒诱导的基因沉默Ha‐ROXL还会在磁盘和射线花发育中造成缺陷。Ha‐ROXL mRNA积累在叶片和AM的近轴边界。在花序发育过程中，Ha‐ROXL在细小弧形细胞中表达，然后在背面片和圆盘花原基之间清晰分离。没有哈ROXL表达积聚在MF花序。在mf和Ha‐ROXL沉默的植物中差异表达了一些已知在植物结构，植物生长素运输和花发育中起作用的基因。这些结果突显了Ha‐ROXL在调节向日葵AM中的主要作用。在双子叶植物，MF是第一个突变体，其启动花分生组织也需要ROXL基因。