Organ size and shape are precisely regulated to ensure proper function. The four sepals in each Arabidopsis thaliana flower must maintain the same size throughout their growth to continuously enclose and protect the developing bud. Here we show that DEVELOPMENT RELATED MYB-LIKE 1 (DRMY1) is required for both timing of organ initiation and proper growth, leading to robust sepal size in Arabidopsis. Within each drmy1 flower, the initiation of some sepals is variably delayed. Late-initiating sepals in drmy1 mutants remain smaller throughout development, resulting in variability in sepal size. DRMY1 focuses the spatiotemporal signalling patterns of the plant hormones auxin and cytokinin, which jointly control the timing of sepal initiation. Our findings demonstrate that timing of organ initiation, together with growth and maturation, contribute to robust organ size.

器官的大小和形状都经过精确调节，以确保功能正常。每个拟南芥花中的四个萼片在整个生长过程中必须保持相同的大小，以不断地封闭和保护发育中的芽。在这里，我们显示发育相关的MYB样1（DRMY1）是器官启动和适当生长的时机所必需的，从而导致拟南芥中健壮的萼片大小。在每朵drmy1花朵中，某些萼片的萌发会有所延迟。drmy1中的晚期启动萼片突变体在整个发育过程中保持较小，导致萼片大小可变。DRMY1着重于植物激素生长素和细胞分裂素的时空信号传导模式，它们共同控制萼片的启动时间。我们的研究结果表明，器官启动的时机，以及生长和成熟，有助于健壮的器官大小。