Phyllotaxy: Beyond the Meristem and Auxin Comes the miRNA.

Phyllotaxy, the arrangement of organs along the stem, has puzzled scientists for centuries. The shoot apical meristem plays a crucial role in the formation of this pattern, by initiating organ primordia on its flanks in a temporally and spatially controlled manner. Recent studies have shown that primordium position at the meristem is governed by local auxin gradients, but little is known about the subsequent events leading to the phyllotaxy along the mature stem.In a recent report we showed that deviation from the initial phyllotaxy set-up in the meristem is generated during stem growth of transgenic lines affected in miR164-mediated regulation of CUC2 and, to a smaller extent, of wild-type Arabidopsis. This underlines the requirement of maintaining the pattern initiated at the meristem during stem development. In this addendum, we discuss the importance of this mechanism in different mutants and at different stages of Arabidopsis development.