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Abstract:
TCPs are a plant specific transcription factor family with 24 members in
Arabidopsis thaliana, sharing a TCP domain involved in DNA binding. We have
previously reported that five TCP genes are regulated by miRNAs. The jaw-D
mutant overexpresses miR-JAW (miR-319a), which causes degradation of
this group of TCPs, leading to crinkly leaves .
We show here that KOs for TCP2, 4 and 10 have larger leaves than wild
type. The TCP2/4 double KO has an even more pronounced leaf phenotype,
resembling that of weak miR-JAW overexpressing lines. In addition, TCP4
mutants flower late, as does the jaw-D mutant.
We have analysed in more detail the regulation of TCP2 and TCP4. The TCP2
promoter is active in leaves and floral organs, while the TCP4 promoter is
active in the vasculature of cotyledons and young leaves. Expression of the
reporters is increased in jaw-D, suggesting that promoter regulation involves
a miRNA-dependent feed back loop. The miRNA-regulated TCPs also contain
a long 5’ UTR, with several AUGs. Deletion of the 5’ UTR causes both an
enhancement of reporter expression and ectopic activation. Taken together
these results suggest that this group of TCPs is regulated at multiple levels,
including transcriptional and post-transcriptional steps.
In a second approach to understand the biological role of the TCPs, miRNAresistant
TCPs (rTCPs) were generated. Expression of rTCP4 under the
control of TCP4 regulatory sequences is mostly lethal. rTCP2 plants survive,
with smaller and rounder leaves, which is roughly the opposite of TCP2 KO
plants. rTCP2 plants also have longer hypocotyls and reduced fertility.
The gain- and loss-of-function phenotypes of TCP2 and TCP4 highlight both
common and differential activities of the miRNA-regulated TCPs.
