AUTHOR=Si Xiaolin , Lyu Shiheng , Hussain Quaid , Ye Hongyu , Huang Chunying , Li Yan , Huang Jianqin , Chen Jianjun , Wang Ketao 

TITLE=Analysis of Delta(9) fatty acid desaturase gene family and their role in oleic acid accumulation in Carya cathayensis kernel

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1193063

DOI=10.3389/fpls.2023.1193063

ISSN=1664-462X

ABSTRACT=<p><italic>Carya cathayensis</italic>, commonly referred to as Chinese hickory, produces nuts that contain high-quality edible oils, particularly oleic acid (18:1). It is known that stearoyl-ACP desaturase (SAD) is the first key step converting stearic acid (C18:0, SA) to oleic acid (C18:1, OA) in the aminolevulinic acid (ALA) biosynthetic pathway and play an important role in OA accumulation. Thus far, there is little information about <italic>SAD</italic> gene family in <italic>C. cathayensis</italic> and the role of individual members in OA accumulation. This study searched the Chinese Hickory Genome Database and identified five members of <italic>SAD</italic> genes, designated as <italic>CcSADs</italic>, at the whole genome level through the comparison with the homologous genes from <italic>Arabidopsis</italic>. RNA-Seq analysis showed that <italic>CcSSI2-1, CcSSI2-2</italic>, and <italic>CcSAD6</italic> were highly expressed in kernels. The expression pattern of <italic>CcSADs</italic> was significantly correlated with fatty acid accumulation during the kernel development. In addition, five full-length cDNAs encoding <italic>SADs</italic> were isolated from the developing kernel of <italic>C. cathayensis</italic>. CcSADs-green fluorescent protein (GFP) fusion construct was infiltrated into tobacco epidermal cells, and results indicated their chloroplast localization. The catalytic function of these <italic>CcSADs</italic> was further analyzed by heterologous expression in <italic>Saccharomyces cerevisiae</italic>, <italic>Nicotiana benthamiana</italic>, and walnut. Functional analysis demonstrated that all <italic>CcSADs</italic> had fatty acid desaturase activity to catalyze oleic acid biosynthesis. Some members of <italic>CcSADs</italic> also have strong substrate specificity for 16:0-ACP to synthesize palmitoleic acid (C16:1, PA). Our study documented <italic>SAD</italic> gene family in <italic>C. cathayensis</italic> and the role of <italic>CcSSI2-1, CcSSI2-2</italic>, and <italic>CcSAD6</italic> in OA accumulation, which could be important for future improvement of OA content in this species via genetic manipulation.</p>