Epistatic repression of PHANTASTICA and class 1 KNOTTED genes is uncoupled in tomato.

Class 1 KNOTTED genes (KNOX) and PHANTASTICA (PHAN) are both central to meristem establishment and maintenance and, in maize and Antirrhinum, it has been proposed that PHAN acts as an epigenetic repressor of KNOX. In tomato, a distinct spatial distribution of Tkn2 KNOX transcripts compared to Antirrhinum and maize suggests either a different spatial distribution of tomato PHAN (Le-phan) transcripts, or that PHAN alone is insufficient for KNOX repression in tomato. We established the pattern of Le-phan expression, including a first demonstration of PHAN expression in healthy roots, and found Le-phan and Tkn2 transcripts to be temporally and spatially coincidental, with PHAN exhibiting an expression pattern in tomato distinct from that in plants with simple leaves. Our results imply that the expression of Le-phan is insufficient for the repression of Tkn2 in tomato and suggest an expanded role for either gene in the establishment of cell identity in plant development.