By Long Wang, Chuan‐Miao Zhou | March 6, 2019
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Age‐dependent development of leaf hairs (trichomes) on the abaxial (lower) leaf surface in Arabidopsis is regulated by integration of positional and temporal cues via a transcriptional complex comprising the leaf abaxial fate determinant KAN1 and the AP2‐like transcription factor TOE1 acting as a developmental timer.
- AP2‐like proteins, including TOE1, repress abaxial trichome formation in juvenile leaves.
- TOE1 forms a repressive complex with KAN1.
- KAN1‐ complex binds to the 3′ downstream sequence of GL1, a master regulator of leaf trichome production.
- KAN1/TOE1 represses GL1 expression through chromatin‐loop mediated histone deacetylation.
Heteroblasty refers to a phenomenon that a plant produces morphologically or functionally different lateral organs in an age‐dependent manner. In the model plant Arabidopsis thaliana, the production of trichomes (epidermal leaf hairs) on the abaxial (lower) side of leaves is a heteroblastic mark for the juvenile‐to‐adult transition. Here, we show that the heteroblastic development of abaxial trichomes is regulated by a spatiotemporally regulated complex comprising the leaf abaxial fate determinant (KAN1) and the developmental timer (miR172‐targeted AP2‐like proteins). We provide evidence that a short‐distance chromatin loop brings the downstream enhancer element into close association with the promoter elements of GL1, which encodes a MYB transcription factor essential for trichome initiation. During juvenile phase, the KAN1‐AP2 repressive complex binds to the downstream sequence of GL1 and represses its expression through chromatin looping. As plants age, the gradual reduction in AP2‐like protein levels leads to decreased amount of the KAN1‐AP2 complex, thereby licensing GL1 expression and the abaxial trichome initiation. Our results thus reveal a novel molecular mechanism by which a heteroblastic trait is governed by integrating age and leaf polarity cue in plants.