AUTHOR=Wan Quan , Bai Tingting , Liu Minmin , Liu Ying , Xie Yating , Zhang Tao , Huang Min , Zhang Jinlian 

TITLE=Comparative Analysis of the Chalcone-Flavanone Isomerase Genes in Six Citrus Species and Their Expression Analysis in Sweet Orange (Citrus sinensis)

JOURNAL=Frontiers in Genetics

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2022.848141

DOI=10.3389/fgene.2022.848141

ISSN=1664-8021

ABSTRACT=<p><italic>Citrus</italic> fruit contains rich nutrients which is edible and of officinal value. <italic>Citrus</italic> flavanones are widely used in the treatment of cardiovascular and other diseases, and they are a foundational material of Chinese medicine. The chalcone-flavanone isomerase (CHI) plays a key role in flavanone synthesis. Therefore, we comprehensively analyzed <italic>CHI</italic> genes in <italic>Citrus</italic> species. Here, thirty <italic>CHI</italic> genes were identified for the first time in six <italic>Citrus</italic> species, which were divided into <italic>CHI</italic> and <italic>FAP</italic> groups. Evolutionary analysis showed that <italic>CHI</italic> gene members were highly conserved and were an ancient family. All <italic>CsCHI</italic> genes showed the highest expression level after the second physiological fruit-falling period in <italic>C. sinensis</italic>. <italic>CsCHI1</italic> and <italic>CsCHI3</italic> were highly expressed at 50 days after the flowering (DAF) stage in albedo. The expression of <italic>CsFAP2</italic> and <italic>CsCHI3</italic> genes at the 50 DAF stage was 16.5 and 24.3 times higher than that at the 220 DAF stage, respectively. The expression of <italic>CsCHI1</italic>, <italic>CsCHI3,</italic> and <italic>CsFAP2</italic> genes in the peel was higher than that in the pulp, especially in common sweet orange. The <italic>CsCHI3</italic> gene maintained a high expression level in the epicarp and juice sac at all periods. The members of CHIs interacted with chalcone synthase (CHS), flavonol synthase/flavanone 3-hydroxylase (FLS) and naringenin, and 2-oxoglutarate 3-dioxygenase (F3H) to form heterodimers, which might together play a regulatory role and participate in the flavonoid pathway. This study will provide the basis for the selection of flavonoids in plant tissues and periods and fundamental information for further functional studies.</p>