Three Arabidopsis Fatty Acyl-Coenzyme A Reductases, FAR1, FAR4, and FAR5, Generate Primary Fatty Alcohols Associated with Suberin Deposition      

Abstract

Suberin is a protective hydrophobic barrier consisting of phenolics, glycerol, and a variety of fatty acid derivatives, including C18:0-C22:0 primary fatty alcohols. An eight-member gene family encoding alcohol-forming fatty acyl-coenzyme A reductases (FARs) has been identified in Arabidopsis (Arabidopsis thaliana). Promoter-driven expression of the b-glucuronidase reporter gene indicated that three of these genes, FAR1 (At5g22500), FAR4 (At3g44540), and FAR5 (At3g44550), are expressed in root endodermal cells. The three genes were transcriptionally induced by wounding and salt stress. These patterns of gene expression coincide with known sites of suberin deposition. We then characterized a set of mutants with T-DNA insertions in FAR1, FAR4, or FAR5 and found that the suberin compositions of roots and seed coats were modified in each far mutant. Specifically, C18:0-OH was reduced in far5-1, C20:0-OH was reduced in far4-1, and C22:0-OH was reduced in far1-1. We also analyzed the composition of polymer-bound lipids of leaves before and after wounding and found that the basal levels of C18:0-C22:0 primary alcohols in wild-type leaves were increased by wounding. In contrast, C18:0-OH and C22:0-OH were not increased by wounding in far5-1 and far1-1 mutants, respectively. Heterologous expression of FAR1, FAR4, and FAR5 in yeast confirmed that they are indeed active alcohol-forming FARs with distinct, but overlapping, chain length specificities ranging from C18:0 to C24:0. Altogether, these results indicate that Arabidopsis FAR1, FAR4, and FAR5 generate the fatty alcohols found in root, seed coat, and wound-induced leaf tissue.

Apoplastic Diffusion Barriers in Arabidopsis

“…For example, localized suberization is modified in response to drought, salinity or wounding. Consistent with these observations, the suberin biosynthetic genes are transcriptionally activated by the same environmental factors Lee et al, 2009;Domergue et al, 2010). The BDG, LACS2 and PEC1 genes that are involved in cutin deposition are also transcriptionally upregulated by drought and abscisic acid Cuticle formation is regulated during organ development and by environmental factors.…”

“…FAR2 (At3g11980) and FAR3/CER4 (At4g33790) are involved in sporopollenin and epidermal wax production, respectively (Rowland et al, 2006;Chen et al, 2011b). The analysis of mutants of endodermis-expressed FARs demonstrated chain-length-specific reductions in the alcohols of root suberin (Domergue et al, 2010). C18 alcohol was reduced in the far5 (At3g44550) mutant, C20 alcohol was reduced in the far4 (At3g44540) mutant and C22 alcohol was reduced in the far1 (At5g22500) mutant.…”

Analyses of Tomato Fruit Brightness Mutants Uncover Both Cutin-Deficient and Cutin-Abundant Mutants and a New Hypomorphic Allele of GDSL Lipase

“…The disc was then delipidated by successive deeps in chloroform/methanol (C/M), at different ratios: C/M (2:1) for 24 h, C/M (1:1) for 24 h, C/M (1:2) for 24 h, and 100% methanol for 24 h. The delipidated epidermis disc was dried for 48 h under pulsed air and for 48 h in a desiccator. Cutin was then depolymerized, analyzed, and quantified as previously described (Domergue et al, 2010).…”

“…The same gene families as for cutin likely contribute to suberin formation (Franke et al, 2012), which also includes specific steps such as fatty acid elongation involving b-keto acyl-CoA synthases and primary alcohol synthesis implicating fatty acyl reductases (Domergue et al, 2010). Likewise, several major enzymes of wax biosynthesis were only recently identified (Bernard and Joubès, 2013).…”

MYB107 and MYB9 Homologs Regulate Suberin Deposition in Angiosperms

“…Thus far, several genes encoding enzymes involved in suberin biosynthesis have been described, including b-KETOACYL-CoA SYNTHASEs (KCS2/DAISY Lee et al, 2009] and KCS20 [Lee et al, 2009]), fatty acid cytochrome P450 oxidases (CYP86A1 [Höfer et al, 2008] and CYP86B1 [Compagnon et al, 2009;Molina et al, 2009]), FATTY ACYL-COA REDUCTASEs (FARs; Domergue et al, 2010;Vishwanath et al, 2013), and GLYCEROL-3-PHOSPHATE ACYLTRANSFERASE5 (GPAT5; Beisson et al, 2007;Li et al, 2007), as well as those responsible for aromatic monomer inclusion, such as ALIPHATIC SUBERIN FERULOYL TRANSFERASE (ASFT; Gou et al, 2009;Molina et al, 2009). Recently, ATP BINDING CASSETTE G transporters (ABCG2, ABCG6, and ABCG20) have been shown to be required for suberin formation (Yadav et al, 2014).…”