Plant circadian clock generates rhythms with a period close to 24 h, and it controls a wide variety of physiological and developmental events, including the transition to reproductive growth (or flowering). During the last decade, significant research progress in
Arabidopsis thaliana has been made in defining the molecular mechanism by which the circadian clock regulates flowering time in response to changes in photoperiod. In
Lotus japonicus, we have found that
LjFTa, which encodes a ortholog of the
Arabidopsis FLOWERING LOCUS T (FT), plays an important role in the promotion of flowering, but it is not clear how the expression of
LjFTa is regulated in
L. japonicus. Based on current knownledge of photoperiodic control of flowering time in
A. thaliana, here we examined whether a microRNA is involved in the activation of
LjFTa in
L. japonicus. Two putative
L. japonicus genes that are responsible for the production of miR172 (designated
LjmiR172a and
LjmiR172b) were cloned. Overexpression of
LjmiR172a/b in
A. thaliana resulted in markedly accelerated flowering through enhancement of the expression of
FT, concomitantly reducing the expression level of
TARGET OF EARLY ACTIVATION TAGGED 1 (
TOE1) transcripts, the protein product of which functions as a transcriptional repressor of
FT. These results suggest that
LjmiR172 genes play a positive role in the
LjFTa-mediated promotion of flowering in
L. japonicus.
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