Flowering is the primary trait affected by ambient
temperature changes. Plant microRNAs
(miRNAs) are small non-coding RNAs playing an
important regulatory role in plant development. In
this study, to elucidate the mechanism of
flowering-time regulation by small RNAs, we
identified six ambient temperature-responsive
miRNAs (miR156, miR163, miR169, miR172, miR398
and miR399) in Arabidopsis via miRNA microarray
and northern hybridization analyses. We also determined
the expression profile of 120 unique miRNA
loci in response to ambient temperature changes by
miRNA northern hybridization analysis. The expression
of the ambient temperature-responsive
miRNAs and their target genes was largely
anticorrelated at two different temperatures (16
and 23 C). Interestingly, a lesion in short vegetative
phase (SVP), a key regulator within the
thermosensory pathway, caused alteration in the
expression of miR172 and a subset of its target
genes, providing a link between a thermosensory
pathway gene and miR172. The miR172-
overexpressing plants showed a temperatureindependent
early flowering phenotype, suggesting
that modulation of miR172 expression leads to temperature
insensitivity. Taken together, our results
suggest a genetic framework for flowering-time regulation
by ambient temperature-responsive
miRNAs under non-stress temperature conditions
