As in animals, plants undergo the juvenile-to-adult developmental transition. Adult plants differ from juvenile plants in terms of leaf shape and reproductive potential. Previous studies have revealed that the juvenile-to-adult transition is under control of an evolutionally conserved small RNA, named miR156. miR156 is highly abundant at the juvenile stage and subsequently declines along with development, thereby licensing the transit to the adult stage. However, how miR156 senses the age of a plant and why the decline of miR156 with age is inevitable remain largely unknown.

 

Just coming out in the journal Proceedings of the National Academy of Sciences, WANG and his colleagues now reveal that cell division in the apical meristem, where stem cells reside, acts as a proxy for chronological age to regulate miR156 decline in A. thaliana. This finding suggests that the maturation speed of a plant is actually determined by cell division rate of the stem cells. More importantly, this simple model provides a plausible explanation of why the maturation program of a multicellular organism is unidirectional and irreversible, and implies that cell quiescence is the fountain of youth in plants.

 

Being a fundamental biological process that integrates both internal and external signals, cell division can serve as an intrinsic developmental timer to modulate plant growth. Interestingly, the division-dependent miR156 decline is reminiscent of replicative aging in yeast. Thus, it will be interesting to see whether such a paradigm is also adopted for other organisms.