Non-cell-autonomous microRNA165 acts in a dose-dependent manner to regulate multiple differentiation status in the Arabidopsis root

Abstract

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.

Literature review of baseline information to support the risk assessment of RNAi‐based GM plants

“…In addition, the levels of three mature miRNAs known to respond to nutrient deprivation in non-vascular tissue, MIR395 (sulphate), MIR398 (copper) and MIR399 (phosphate), were increased in phloem sap during the growth of plants under the respective nutrient deprivation . Other known mobile miRNAs in Arabidopsis are MIR394, which is produced by the surface cell layer and contributes to shoot meristem formation (Knauer et al, 2013), and MIR165, which regulates differentiation (Miyashima et al, 2011).…”

Cell-to-cell communication via plasmodesmata in vascular plants

“…Conversely, inducing MIR165A expression in the stele reduces PHB expression and leads to ectopic protoxylem development. 8 Miyashima et al 9 further identified miR166A as a third miRNA expressed in the endodermis in a SCR-dependent manner, and that MIR166A and MIR166B are expressed in the QC in addition to the endodermis. Importantly, the authors also demonstrated that miR165 restricts the PHB expression domain and xylem differentiation in a dose-dependent manner.…”

“…In addition, PHB restriction mediated by the miRNAs is necessary for pericycle differentiation, as in both phb1d and scr-3 the expression of two pericycle identity markers, AHP6 and SKOR, is reduced in the pericycle domain. 9 Thus, stele and the groundtissue exchange information via mobile SHR and miR165/6 species to coordinate each other's development.…”

Requirement of MIR165A primary transcript sequence for its activity pattern in Arabidopsis leaf primordia

“…Requirement of MIR165A primary transcript sequence for its activity pattern in Arabidopsis leaf primordia Kiyoshi Tatematsu 1, * , Koichi Toyokura 2 , and Kiyotaka Okada 3,4 1 National Institute for Basic Biology; Okazaki, Japan; 2 Graduate School of Science; Kobe University; Kobe, Japan; 3 Department of Agriculture; Ryukoku University; Otsu, Japan; 4 National Institute of Natural Science; Tokyo, Japan m iRNAs might move cell to cell and act as mobile signals in plant development, while the regulatory mechanisms of miRNA cell-to-cell movement are still unclear. Recently, in Arabidopsis leaf primordia, we revealed that miR165 from the MIR165A gene, which is expressed in the abaxial epidermal cells of leaf primordia, acts non-cell-autonomously in inner cells on the abaxial side.…”

“…2 In Arabidopsis roots, miR165/166-encoding genes, MIR165A, MIR166A and MIR166B, are expressed in the endodermis and miR165/166 is likely to move to the stele to repress HD-Zip III expression. 3,4 MIR165/166 genes also show non-cell-autonomous activity during embryogenesis. 5 These data indicate that miRNAs are able to act as mobile signals for development.…”