75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

221 The distribution of microRNA165/166 in Arabidopsis involves ASYMMETRIC LEAVES2 and
histone deacetylase
Yoshihisa Ueno 1 , Chiyoko Machida 2 , Yasunori Machida 1
1
Nagoya University, 2 Chubu University
Tissue-specific expression of microRNAs (miRNAs) plays important roles in the development of multicellular
organisms. miRNAs are transcribed as long precursors and are processed by factors that include Dicer-family proteins.
However, the regulation of tissue-specific expression of miRNA is poorly understood. Here, we present evidence that
the ASYMMETRIC LEAVES2 (AS2), ASYMMETRIC LEAVES1 (AS1), HDT1/HD2A and HDT2/HD2B proteins, all
localized to nuclei, control the abaxial (peripheral) distribution of miR165 and/or miR166 (miR165/166) and, consequently,
the polarity of Arabidopsis leaves. Following treatment with inhibitors of histone deacetylases (HDACs), as1 and as2
mutants frequently formed abaxialized filamentous leaves. Our reporter gene showed that the distribution of miR165/166
is deregulated in these mutants, especially on the adaxial side of leaves, in addition to the inhibition of HDAC activity.
It is known that PHABULOSA (PHB) and REVOLUTA (REV) are negatively regulated by miR165/166 and positively
regulate cell identity on the adaxial side of leaves. The recessive REV mutation enhanced the phenotypes of as1 and as2
mutants. The mutation of HASTY (HST), which positively regulates the accumulation of miRNAs, partially suppressed
the phenotypes of as1 and as2 mutants. The dominant phb-1D mutation, whose transcripts are resistant to miR165/166,
was epistatic to the as2 mutation. Inducible ectopic overproduction of AS2 protein caused decreased accumulation of
miR165/166 and ectopic accumulation of PHB transcripts. The reduction of miR165/166 by AS2 required AS1 and HDAC
activity. AS2 is expressed on the adaxial side of young leaves. Thus, AS2 together with AS1 and HDAC(s) control the
distribution of miR165/166 in leaves of Arabidopsis. Furthermore, we developed RNA interference (RNAi) libraries
specific to HDACs and identified HDT1/HD2A and HDT2/HD2B as the relevant factors. HDT1/HD2A and HDT2/HD2B
encode the HDACs involved in the regulation of chromatin status. Our findings suggest that these unexpected factors
control the specific spatial expression of miRNAs.
222 Addressing the Movement and Possible Target of the bypass1 Root-Derived Signal
Jaimie Van Norman, Leslie Sieburth
University of Utah
Plants with a mutation in the BYPASS1 (BPS1) gene exhibit defects in root development and arrest of apical
development. Root excision and grafting experiments revealed that bps1 (mutant) apical development proceeds normally
in the absence of the bps1 (mutant) root, and the bps1 root is sufficient to arrest leaf expansion and initiation in the wild
type 1 . These data suggest a model where BPS1 negatively regulates production of a root-to-shoot signal that inhibits
apical development. BPS1 encodes a novel plant specific protein of unknown function and contains no functionally
characterized domains. We have used genetics and inhibitors to characterize the bps1 root-derived signal; our data indicate
bps1 mutants produce a novel carotenoid-derived signal 2 .
To understand more about the production and movement of the bps1 root-derived signal we are taking genetic and
reporter gene approaches. We have replicated our surgical ablation of the bps1 root genetically, by generating double
mutants with ROOT MERISTEMLESS1 (RML1). rml1 seedlings lack post-embryonic cell division in the root 3 , with
only modest shoot defects. Our data show bps1 leaf development is rescued in bps1 rml1 double mutants, confirming
our previous surgical data.
How does the bps1 signal reach the shoot We reasoned that movement could occur through the xylem or phloem,
or by cell-to-cell movement. To distinguish between these possibilities, we generated double mutants between bps1
and mutants that are defective either in xylem or phloem development. Our data suggests that bps1 signal moves via a
nonvascular route.
Another of our goals is to identify the molecular targets of the bps1 signal in the shoot. We previously showed that
bps1 mutant leaves were unable to activate expression of the DR5::GUS reporter gene when we applied exogenous
auxin (2,4-D) 1 . We are expanding this analysis to include other auxin reporter genes. The results of these studies will
be presented.
1. Van Norman, et al., 2004 Current Biology, 14:1739-1746.
2. Van Norman and Sieburth, 2006, manuscript in preparation.
3. Vernoux, et al., Plant Cell, 12:97-109.