AUTHOR=Ping Chia-Yun , Chen Fure-Chyi , Cheng Teen-Chi , Lin Huey-Ling , Lin Tzong-Shyan , Yang Wen-Ju , Lee Yung-I 

TITLE=Expression Profiles of Phosphoenolpyruvate Carboxylase and Phosphoenolpyruvate Carboxylase Kinase Genes in Phalaenopsis, Implications for Regulating the Performance of Crassulacean Acid Metabolism

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01587

DOI=10.3389/fpls.2018.01587

ISSN=1664-462X

ABSTRACT=<p><italic>Phalaenopsis</italic> is one of the most important potted plants in the ornamental market of the world. Previous reports implied that crassulacean acid metabolism (CAM) orchids at their young seedling stages might perform C<sub>3</sub> or weak CAM photosynthetic pathways, but the detailed molecular evidence is still lacking. In this study, we used a key species in white <italic>Phalaenopsis</italic> breeding line, <italic>Phalaenopsis aphrodite</italic> subsp. <italic>formosana</italic>, to study the ontogenetical changes of CAM performance in <italic>Phalaenopsis</italic>. Based on the investigations of rhythms of day/night CO<sub>2</sub> exchange, malate contents and phosphoenolpyruvate carboxylase (PEPC) activities, it is suggested that a progressive shift from C<sub>3</sub> to CAM occurred as the protocorms differentiated the first leaf. To understand the role of phosphoenolpyruvate carboxylase kinase (PEPC kinase) in relation to its target PEPC in CAM performance in <italic>Phalaenopsis</italic>, the expression profiles of the genes encoding <italic>PEPC</italic> (<italic>PPC</italic>) and <italic>PEPC kinase</italic> (<italic>PPCK</italic>) were measured in different developmental stages. In <italic>Phalaenopsis</italic>, two <italic>PPC</italic> isogenes were constitutively expressed over a 24-h cycle similar to the housekeeping genes in all stages, whereas the significant day/night difference in <italic>PaPPCK</italic> expression corresponds to the day/night fluctuations in PEPC activity and malate level. These results suggest that the <italic>PaPPCK</italic> gene product is most likely involved in regulation of CAM performance in different developmental stages of <italic>Phalaenopsis</italic> seedlings.</p>