Planta (2007) 225:1327–1338
DOI 10.1007/s00425-006-0439-1
123
ORIGINAL ARTICLE
MIR166/165 genes exhibit dynamic expression patterns
in regulating shoot apical meristem and Xoral development
in Arabidopsis
Jae-Hoon Jung · Chung-Mo Park
Received: 21 September 2006 / Accepted: 26 October 2006
/ Published online: 16 November 2006
© Springer-Verlag 2006
Abstract The miR166/165 group and its target genes
regulate diverse aspects of plant development, includ-
ing apical and lateral meristem formation, leaf polarity,
and vascular development. We demonstrate here that
MIR166/165 genes are dynamically controlled in regu-
lating shoot apical meristem (SAM) and Xoral develop-
ment in parallel to the WUSCHEL (WUS)-CLAVATA
(CLV) pathway. Although miR166 and miR165 cleave
same target mRNAs, individual MIR166/165 genes
exhibit distinct expression domains in diVerent plant
tissues. The MIR166/165 expression is also temporarily
regulated. Consistent with the dynamic expression pat-
terns, an array of alterations in SAM activities and
Xoral architectures was observed in the miR166/165-
overproducing plants. In addition, when a MIR166a-
overexpressing mutant was genetically crossed with
mutants defective in the WUS-CLV pathway, the resul-
tant crosses exhibited additive phenotypic eVects, sug-
gesting that the miR166/165-mediated signal exerts its
role via a distinct signaling pathway.
Keywords Arabidopsis · HD-ZIP III · microRNA ·
mRNA cleavage · Shoot apical meristem
Abbreviations
CLV CLAVATA
CNA CORONA
FM Floral meristem
HD-ZIP III Class III homeodomain-leucine zipper
miRNA MicroRNA
PHB PHABULOSA
PHV PHAVOLUTA
REV REVOLUTA
SAM Shoot apical meristem
WUS WUSCHEL
Introduction
Stem cell maintenance is spatially regulated by a nega-
tive feedback loop consisting of CLV3 and WUS (Laux
et al. 1996; Mayer et al. 1998; Rojo et al. 2002). The
WUS signal is transmitted to the stem cells positioned
in the outermost layers and induces CLV3 (Mayer
et al. 1998; Fletcher et al. 1999). The stem cells then
signal back to the organizing center (OC) and maintain
the WUS expression domain (Lenhard and Laux 2003).
Maintenance of the stem cells is also temporarily regu-
lated. The Xoral meristem (FM) activity is regulated by
multiple sets of overlapping regulators, including
CLVs and WUS and a group of transcription factors,
such as LEAFY (LFY) and APETALA1 (AP1) (Wei-
gel and Nilsson 1995; Sharma et al. 2003). Termination
of stem cell activity in the FM is mediated by a tempo-
ral negative feedback loop that requires both Xower
patterning and stem cell maintenance genes (Lenhard
et al. 2001; Gregis et al. 2006).
microRNAs (miRNAs) are important participants
in the regulation of signaling networks involved in stem
cell maintenance (Jones-Rhoades et al. 2006). The
Arabidopsis miR166/165 group targets Wve members of
the HD-ZIP III transcription factor genes, such as
REVOLUTA (REV), PHABULOSA (PHB), PHAVO
LUTA (PHV), CORONA (CNA)/ATHB15, and ATH
B8 and functions by cleaving target mRNAs through
J.-H. Jung · C.-M. Park (&)
Molecular Signaling Laboratory, Department of Chemistry,
Seoul National University, Seoul 151-742, South Korea
e-mail: cmpark@snu.ac.kr