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In the development of multicellular organisms, cell fate is usually determined by exchanging positional information. Animals employ a class of intercellular signaling molecules that specify different cell fates by their dosage, but the existence of an equivalent system has not been demonstrated in plants, except that the growth regulator auxin has been proposed to act in a similar manner in certain developmental contexts. Recently, it has been reported that, in the Arabidopsis root meristem, endodermis-derived microRNA (miR) 165/166 non-cell-autonomously suppress the expression of the Class III HD-ZIP transcription factor PHABULOSA (PHB) in the peripheral stele, thereby specifying xylem differentiation. Here, we show that the miR165/166-dependent suppression of PHB is required not only for xylem specification, but also for differentiation of the pericycle, as well as for ground tissue patterning. Furthermore, using a plant system that allows quantitative control of miR165 production in the ground tissue, we show that endodermis-derived miR165 acts in a dose-dependent manner to form a graded distribution of PHB transcripts across the stele. These results reveal a previously unidentified role of miR165 in the differentiation of a broad range of root cell types and suggest that endodermis-derived miR165 acts in a dose-dependent manner to control multiple differentiation status in the Arabidopsis root.
Miyashima et al. (Tue,) studied this question.