The size of plant lateral organs is determined by well-coordinated cell proliferation and cell expansion. Here, we report that miR159, an evolutionarily conserved microRNA, plays an essential role in regulating cell division in rose (Rosa hybrida) petals by modulating cytokinin catabolism. We uncover that Cytokinin Oxidase/Dehydrogenase6 (CKX6) is a target of miR159 in petals. Knocking down miR159 levels results in the accumulation of CKX6 transcripts and earlier cytokinin clearance, leading to a shortened cell division period and smaller petals. Conversely, knocking down CKX6 causes cytokinin accumulation and a prolonged developmental cell division period, mimicking the effects of exogenous cytokinin application. MYB73, a R2R3-type MYB transcription repressor, recruits a co-repressor (TOPLESS) and a histone deacetylase (HDA19) to form a suppression complex, which regulates MIR159 expression by modulating histone H3 lysine 9 acetylation levels at the MIR159 promoter. Our work sheds light on mechanisms for ensuring the correct timing of the exit from the cell division phase and thus organ size regulation by controlling cytokinin catabolism.

植物侧生器官的大小由协调良好的细胞增殖和细胞扩张决定。在这里，我们报道了 miR159，一种进化上保守的 microRNA，通过调节细胞分裂素分解代谢，在调节玫瑰 ( Rosahyda ) 花瓣的细胞分裂中发挥着重要作用。我们发现细胞分裂素氧化酶/脱氢酶 6 ( CKX6 ) 是花瓣中 miR159 的靶标。降低 miR159 水平会导致CKX6转录物的积累和细胞分裂素的早期清除，从而缩短细胞分裂期并缩小花瓣。相反，敲低CKX6会导致细胞分裂素积累和发育细胞分裂期延长，模仿外源细胞分裂素应用的效果。MYB73 是一种 R2R3 型 MYB 转录阻遏蛋白，它招募辅阻遏蛋白 (TOPLESS) 和组蛋白脱乙酰酶 (HDA19) 形成抑制复合物，通过调节MIR159启动子处的组蛋白 H3 赖氨酸 9 乙酰化水平来调节MIR159表达。我们的工作揭示了确保退出细胞分裂阶段的正确时机的机制，从而通过控制细胞分裂素分解代谢来调节器官大小。