背景回顾：What determines the rate at which a multicellular organism matures is a fundamental question in biology. In plants, the decline of miR156 withageserves as an intrinsic, evolutionarily conserved timer for the juvenile-to-adult phase transition. 

提出问题：However, the way in which age regulates miR156 abundance is poorly understood. 

主要发现：Here, we show that the rate of decline in miR156 is correlated with developmental age rather than chronological age. 

分子机理：Mechanistically, we found that cell division in the apical meristem is a trigger for miR156 decline. The transcriptional activity of MIR156 genes is gradually attenuated by the deposition of the repressive histone mark H3K27me3 along with cell division.

结论：Our findings thus provide a plausible explanation of why the maturation program of a multicellular organism is unidirectional and irreversible under normal growth conditions and suggest that cell quiescence is the fountain of youth in plants.

 摘 要 

在生物学中，什么决定了多细胞生物成熟速度是一个十分重要且基础的问题。在植物中，miR156随着年龄的增长而下降，作为一种内源的、演化上保守的生物计时器，控制植物从幼年向成年的发育时期转变。但是，年龄又是如何调控miR156的丰度还不清楚。本文中，作者发现相比于时间年龄，植物体内的miR156下降速率与发育年龄更加相关。机理上，作者发现顶端分生组织中的细胞分裂是miR156下降的诱导因素。MIR156基因的转录活性随着细胞分裂，受到抑制性组蛋白修饰H3K27me3沉积而导致的逐渐减弱。本文的研究发现为正常生长条件下多细胞生物的成熟程序在是单向且不可逆提供了一个合理的解释，并且表明细胞静止是植物“永葆”青春的源泉。