AUTHOR=Jiang Lan , Song Cheng , Zhu Xi , Yang Jianke 

TITLE=SWEET Transporters and the Potential Functions of These Sequences in Tea (Camellia sinensis)

JOURNAL=Frontiers in Genetics

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2021.655843

DOI=10.3389/fgene.2021.655843

ISSN=1664-8021

ABSTRACT=<p>Tea (<italic>Camellia sinensis</italic>) is an important economic beverage crop. Its flowers and leaves could be used as healthcare tea for its medicinal value. SWEET proteins were recently identified in plants as sugar transporters, which participate in diverse physiological processes, including pathogen nutrition, seed filling, nectar secretion, and phloem loading. Although <italic>SWEET</italic> genes have been characterized and identified in model plants, such as <italic>Arabidopsis thaliana</italic> and <italic>Oryza sativa</italic>, there is very little knowledge of these genes in <italic>C. sinensis</italic>. In this study, 28 <italic>CsSWEET</italic>s were identified in <italic>C. sinensis</italic> and further phylogenetically divided into four subfamilies with <italic>A. thaliana</italic>. These identified <italic>CsSWEET</italic>s contained seven transmembrane helixes (TMHs) which were generated by an ancestral three-TMH unit with an internal duplication experience. Microsynteny analysis revealed that the large-scale duplication events were the main driving forces for members from <italic>CsSWEET</italic> family expansion in <italic>C. sinensis</italic>. The expression profiles of the 28 <italic>CsSWEET</italic>s revealed that some genes were highly expressed in reproductive tissues. Among them, <italic>CsSWEET1a</italic> might play crucial roles in the efflux of sucrose, and <italic>CsSWEET17b</italic> could control fructose content as a hexose transporter in <italic>C. sinensis</italic>. Remarkably, <italic>CsSWEET12</italic> and <italic>CsSWEET17c</italic> were specifically expressed in flowers, indicating that these two genes might be involved in sugar transport during flower development. The expression patterns of all <italic>CsSWEET</italic>s were differentially regulated under cold and drought treatments. This work provided a systematic understanding of the members from the <italic>CsSWEET</italic> gene family, which would be helpful for further functional studies of <italic>CsSWEET</italic>s in <italic>C. sinensis</italic>.</p>