PeERF1, a SHINE-Like Transcription Factor, Is Involved in Nanoridge Development on Lip Epidermis of Flowers.

orchids have a spectacular floral morphology with a highly evolved lip that offers a landing platform for pollinators. The typical morphological orchid lip features are essential for the special pollination mechanism of flowers. Previously, we found that in the lip, a member of the AP2/EREBP protein family was highly expressed. Here, we further confirmed its high expression and characterized its function during lip development. Phylogenetic analysis showed that AP2/EREBP belongs to the Va2 subgroup of ERF transcription factors. We named it PeERF1. We found that was only expressed at stage 5, as flowers opened. This coincided with both thickening of the cuticle and development of nanoridges. We performed knockdown expression of using CymMV-based virus-induced gene silencing in either the conserved domain, producing -silenced plants, or the specific domain, producing silenced plants. Using cryo-SEM, we found that the number of nanoridges was reduced only in the -silenced group. This change was found on both the abaxial and adaxial surfaces of the central lip lobe. Expression of was reduced significantly in -silenced plants. In cutin biosynthesis genes, expression of both and was significantly decreased in both groups. The expression of was reduced significantly only in the -silenced plants. Although expression was reduced in both silenced plants, but to a lesser degree. The expression of was significantly reduced in the petal-like lip of a big-lip variant. and in the lip were also reduced, but . Furthermore, heterologous overexpression of in the genus produced leaves that were shiny on the adaxial surface. Taken together, our results show that in orchids PeERF1 plays an important role in formation of nanoridges during lip epidermis development.