Ectopic Expression of CsKCS6 From Navel Orange Promotes the Production of Very-Long-Chain Fatty Acids (VLCFAs) and Increases the Abiotic Stress Tolerance of Arabidopsis thaliana.

Qi Wu,Li Yang,Dechun Liu,Yong Liu,Wenfang Guo,Wei Hu

doi:10.3389/fpls.2020.564656

Abstract

Cuticular wax is closely related to plant resistance to abiotic stress. 3-Ketoacyl-CoA synthase (KCS) catalyzes the biosynthesis of very-long-chain fatty acid (VLCFA) wax precursors. In this study, a novel KCS family gene was isolated from Newhall navel orange and subsequently named CsKCS6. The CsKCS6 protein has two main domains that belong to the thiolase-like superfamily, the FAE1-CUT1-RppA and ACP_syn_III_C domains, which exist at amino acid positions 80–368 and 384–466, respectively. CsKCS6 was expressed in all tissues, with the highest expression detected in the stigma; in addition, the transcription of CsKCS6 was changed in response to drought stress, salt stress and abscisic acid (ABA) treatment. Heterologous expression of CsKCS6 in Arabidopsis significantly increased the amount of VLCFAs in the cuticular wax on the stems and leaves, but there were no significant changes in total wax content. Compared with that of the wild-type (WT) plants, the leaf permeability of the transgenic plants was lower. Further research showed that, compared with the WT plants, the transgenic lines experienced less water loss and ion leakage after dehydration stress, displayed increased survival under drought stress treatment and presented significantly longer root lengths and survival under salt stress treatment. Our results indicate that CsKCS6 not only plays an important role in the synthesis of fatty acid precursors involved in wax synthesis but also enhances the tolerance of transgenic Arabidopsis plants to abiotic stress. Thus, the identification of CsKSC6 could help to increase the abiotic stress tolerance of Citrus in future breeding programs.

Highlights

Very-long-chain fatty acids (VLCFAs), which refer mainly to a class of fatty acids with more than 18 carbon atoms, are precursor materials for the synthesis of plant cuticular waxes (Kunst and Samuels, 2003)
Further study revealed that the expression level of CsKCS6 in ‘Ganqi 3’ fruit peels were significant lower than that in ‘Newhall’ fruit peels, indicating the CsKCS6 might be involved in cuticular wax biosynthesis (Liu et al, 2016)
Structural analysis revealed that the FAE1-CUT1-RppA conserved domain was found at amino acid positions of 80– 368 in CsKCS6 and that the ACP_syn_III_C conserved domain was found at 384–466

Summary

Introduction

Very-long-chain fatty acids (VLCFAs), which refer mainly to a class of fatty acids with more than 18 carbon atoms, are precursor materials for the synthesis of plant cuticular waxes (Kunst and Samuels, 2003). FAE1, which is expressed only in seeds, was the first KCS family gene cloned from Arabidopsis, and its encoded protein catalyzes the synthesis of C20 and C22 fatty acids and storage lipids (James et al, 1995). FDH is expressed mainly in the flowers and young leaves of Arabidopsis; the FDH gene participates in the synthesis of VLCFAs in epidermal cells and is involved in both the regulation of plant morphological structure and the response to biotic stress (Yephremov et al, 1999; Pruitt et al, 2000; Joubès et al, 2008). Its functional defect mutant cer accumulated a large quantity of C24 VLCFA derivatives, indicating that this gene is involved in the biosynthesis of C24 (or longer) VLCFAs (Millar et al, 1999; Fiebig et al, 2000; Hooker et al, 2002)

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