Identification of Chalcone Isomerase Family Genes and Roles of CnCHI4 in Flavonoid Metabolism in Camellia nitidissima

Abstract

<i>Camellia nitidissima</i> is a woody plant with high ornamental value, and its golden-yellow flowers are rich in a variety of bioactive substances, especially flavonoids, that are beneficial to human health. Chalcone isomerases (CHIs) are key enzymes in the flavonoid biosynthesis pathway; however, there is a scarcity of information regarding the <i>CHI</i> family genes of <i>C. nitidissima</i>. In this study, seven <i>CHI</i> genes of <i>C. nitidissima</i> were identified and divided into three subfamilies by phylogenetic analysis. The results of multiple sequence alignment revealed that, unlike CnCHI1/5/6/7, CnCHI2/3/4 are bona fide CHIs that contain all the active site and critical catalytic residues. Analysis of the expression patterns of <i>CnCHIs</i> and the total flavonoid content of the flowers at different developmental stages revealed that <i>CnCHI4</i> might play an essential role in the flavonoid biosynthesis pathway of <i>C. nitidissima</i>. <i>CnCHI4</i> overexpression significantly increased flavonoid production in <i>Nicotiana tabacum</i> and <i>C. nitidissima</i>. The results of the dual-luciferase reporter assay and yeast one-hybrid system revealed that CnMYB7 was the key transcription factor that governed the transcription of <i>CnCHI4</i>. The study provides a comprehensive understanding of the <i>CHI</i> family genes of <i>C. nitidissima</i> and performed a preliminary analysis of their functions and regulatory mechanisms.