AUTHOR=Zhang Cheng , Yang Jiabao , Meng Wanqiu , Zeng Linglu , Sun Li 

TITLE=Genome-wide analysis of the WSD family in sunflower and functional identification of HaWSD9 involvement in wax ester biosynthesis and osmotic stress

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.975853

DOI=10.3389/fpls.2022.975853

ISSN=1664-462X

ABSTRACT=<p>The wax esters are important cuticular wax composition that cover the outer surface of plant organs and play a critical role in protection and energy metabolism. Wax ester synthesis in plant is catalyzed by a bifunctional wax ester synthase/acyl-CoA: diacylglycerol acyltransferase (WSD). Sunflower (<italic>Helianthus annuus</italic> L.) is an important oil crop in the world; however, little is known about WSD in sunflower. In this study, we identified and performed a functional analysis of twelve <italic>HaWSD</italic> genes from sunflower genome. Tissue-specific expression revealed that 12 <italic>HaWSD</italic> genes were differentially expressed in various organs and tissues of sunflower, except seeds. <italic>HaWSD</italic> genes were highly induced by salinity, drought, cold, and abscisic acid (ABA) in sunflower. To ascertain their function, <italic>HaWSD9</italic>, with highly expressed levels in stems and leaves, was cloned and expressed in a yeast mutant defective in triacylglycerol (TAG) biosynthesis. <italic>HaWSD9</italic> complemented the phenotype by producing wax ester but not TAG <italic>in vivo</italic>, indicating that it functions as a wax ester synthase. Subcellular localization analysis indicated that HaWSD9 was located in the endoplasmic reticulum (ER). Heterologous introduction of <italic>HaWSD9</italic> into Arabidopsis <italic>wsd1</italic> mutant exhibited increased epicuticular wax crystals and cuticular wax contents on the stems. As compared with the <italic>wsd1</italic> mutant, <italic>HaWSD9</italic> overexpressing transgenic Arabidopsis showed less cuticle permeability, chlorophyll leaching and water loss rate. Further analysis showed that the <italic>HaWSD9</italic> transgenics enhanced tolerance to ABA, mannitol, drought and salinity, and maintained higher leaf relative water content (RWC) than the <italic>wsd1</italic> mutant under drought stress, suggesting that <italic>HaWSD9</italic> play an important physiological role in stress response as well as wax synthase. These results contribute to understanding the function of <italic>HaWSD</italic> genes in wax ester synthesis and stress tolerance in sunflower.</p>