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Abstract

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.