What determines the rate at which a multicellular organism ages is a mystery in biology. In plants the changes in morphological and physiological traits serve as markers for the developmental transitions. Mutant characterizations and genetic analyses in Arabidopsis thaliana delineate an evolutionarily conserved, microRNA156 (miR156)-guided timing mechanism that temporally regulates many aspects of biological processes during development. Recent studies now reveal that sugar metabolites, the products of photosynthesis, feed into this developmental timer by regulating miR156 levels, thereby ensuring that each developmental transition occurs under favorable conditions.
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