Skip to main content
. 2019 Oct 22;8(10):433. doi: 10.3390/plants8100433

Figure 2.

Figure 2

Coordination of adaxial–abaxial and proximodistal leaf patterning factors. (A) Longitudinal model cross-section of the leaf with adaxial factors labeled in cyan, abaxial factors labeled in orange, and proximal factors labeled in purple. AS2 and HD-ZIPIII transcripts accumulate in the adaxial domain of the leaf, while ETT/ARF3, ARF4, miR165/166, and KAN transcripts accumulate in the abaxial domain. miR165/166 and the mature ta-siARF RNAs are capable of moving intercellularly and repressing HD-ZIPIII and ETT/ARF3 postranscriptionally. HD-ZIPIII and KAN genetically antagonize one another and AS2 can genetically repress KAN. The AS1–AS2 complex recruits the HIRA protein and the PRC2/LHP1 complex to repress expression of Class I KNOX genes and also directly binds and represses the expression of ETT/ARF3 and miR166 in the adaxial portion of the leaf. AS1–AS2 binds TAS3, which encodes the ta-siARF precursor transcript, possibly as a protective mechanism to exclude TAS3-antagonizing transcription factors from accessing their promoter binding sites. The abaxial factor ETT/ARF3 directly represses the expression of the Class I KNOX gene STM by recruiting HDACs. KAN restricts AS2 expression to the adaxial domain via a direct repressive interaction. (B) Radially organized expression domains of patterning factors within the meristem may prepattern the adaxial–abaxial axis of the leaf. HD-ZIPIII genes are expressed centrally while KAN and miR166 are expressed peripherally. WOX1 expression occurs at the juxtaposition of these domains. The auxin response is restricted to the boundary region where auxin promotes outgrowth of the leaf primordium, retaining the prepatterned domains of gene expression during the establishment of the proximodistal leaf axis.