AUTHOR=Lai Pei-Han , Huang Li-Min , Pan Zhao-Jun , Jane Wann-Neng , Chung Mei-Chu , Chen Wen-Huei , Chen Hong-Hwa 

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

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.01709

DOI=10.3389/fpls.2019.01709

ISSN=1664-462X

ABSTRACT=<p><italic>Phalaenopsis</italic> 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 <italic>Phalaenopsis</italic> 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 <italic>PeERF1</italic> 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 <italic>PeERF1</italic> using CymMV-based virus-induced gene silencing in either the <italic>AP2</italic> conserved domain, producing <italic>PeERF1_AP2</italic>-silenced plants, or the <italic>SHN</italic> specific domain, producing <italic>PeERF1_SHN-</italic>silenced plants. Using cryo-SEM, we found that the number of nanoridges was reduced only in the <italic>PeERF1_AP2</italic>-silenced group. This change was found on both the abaxial and adaxial surfaces of the central lip lobe. Expression of <italic>PeERF1</italic> was reduced significantly in <italic>PeERF1_AP2</italic>-silenced plants. In cutin biosynthesis genes, expression of both <italic>PeCYP86A2</italic> and <italic>PeDCR</italic> was significantly decreased in both groups. The expression of <italic>PeCYP77A4</italic> was reduced significantly only in the <italic>PeERF1_AP2</italic>-silenced plants. Although <italic>PeGPAT</italic> expression was reduced in both silenced plants, but to a lesser degree. The expression of <italic>PeERF1</italic> was significantly reduced in the petal-like lip of a big-lip variant. <italic>PeCYP77A4</italic> and <italic>PeGPAT</italic> in the lip were also reduced, but <italic>PeDCR was not</italic>. Furthermore, heterologous overexpression of <italic>PeERF1</italic> in the genus <italic>Arabidopsis</italic> produced leaves that were shiny on the adaxial surface. Taken together, our results show that in <italic>Phalaenopsis</italic> orchids PeERF1 plays an important role in formation of nanoridges during lip epidermis development.</p>