15th International Conference on Arabidopsis Research - TAIR

T02-031
A suppressor screening of jaw-D, a microRNA
overexpressing mutant
Heike Wollmann(1), Javier Palatnik(1, 2), Detlef Weigel(1, 2)
1-Max-Planck-Institute for Developmental Biology, Tuebingen, Germany
2-Salk Institute, La Jolla, CA 92037, USA
MicroRNAs (miRNAs) are small RNAs with regulatory function in both plants
and animals. Their mode of action requires interaction with target mRNAs
through complementary basepairing. In plants, most miRNAs seem to guide
their mRNA targets to cleavage, causing downregulation of target transcripts.
miR-JAW (miR-319a), like several other miRNAs, plays important roles in
plant development. The jaw-D mutant, which constitutively overexpresses
miR-JAW, shows pleiotropic phenotypes, including epinastic cotyledons,
crinkly leaves and a delay in flowering time. This is due to the simultaneous
downregulation of five genes belonging to the TCP class of plant-specific
transcription factors, which are thought to be involved in the regulation of cell
proliferation.
To gain further insight into the molecular mechanisms responsible for
miR-JAW activity and function, we carried out a suppressor screen in jaw-D
background. We mutagenized 20.000 jaw-D seeds with EMS and screened
the M2-population for plants in which the jaw-D associated phenotypes are
suppressed. 50 putative suppressors were isolated. In some, all phenotypes
of jaw-D mutants are affected, while in others only a subset is affected, like
leaf shape or flowering time. RT-qPCR of the TCPs allows a further classification
of the suppressors, e.g. a low TCP level would imply that the suppressor
acts downstream of the transcription factors. We will describe the phenotypic
and molecular characterization of several suppressor mutants.
T02 Development 2 (Shoot, Root)
T02-032
CUC2 and CUC3 are involved in axillary meristem
formation and post-embryonic organ separation.
Ken-ichir Hibara(1), Masao Tasaka(1)
1-Graduate School of Biological Sciences Nara Institute of Science and Technology (NAIST), Japan
A shoot apical meristem (SAM) formed in embryo constructs a main shoot
after germination and axillary shoot meristems formed in each leaf axils
develop lateral shoots. These meristems are essential for the development of
shoot architecture.
CUC1 and CUC2 were identified as factors regulating SAM formation and
cotyledon separation during embryogenesis.
We have isolated CUC3 (CUP-SHAPED COTYLEDON3) from screening of cuc2
enhancer mutants. CUC3 have a highly conserved NAC domain comparable
with CUC1, 2 but have no conserved C terminal element and micro RNA
recognizing site found in CUC1, 2.
cuc3 single mutant showed an abnormal shoot, lateral shoots occasionally
uncoupled from cauline leaf and there is no axillary shoot meristem at a low
frequency. Additionally, in cuc2 cuc3 double mutant, lateral organs such as
leaves, stems and floral organs were fused each other, indicating that mutation
of CUC2 enhanced cuc3. However, mutation of CUC1 didn’t enhance cuc3
in aerial part. These indicated that CUC2 and CUC3 act redundantly to regulate
axillary meristem formation and organ separation post-embryonically.
CUC2 and CUC3 expressed between SAM and lateral organ after germination.
This expression profile and post-embryonic phenotype are similar to
that of LAS (LATERAL SUPPRESSOR). To understand the genetic interaction
among CUC2, 3 and LAS, we analyzed the double and triple mutants. As a
result, mutation of LAS enhanced both cuc2 and cuc3 single mutant, especially
cuc3 las double mutant showed strong abnormality such as axillary
shoot defect and lateral organ fusion.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin