The glabra1 Mutation Affects Cuticle Formation and Plant Responses to Microbes      

Abstract

Systemic acquired resistance (SAR) is a form of defense that provides resistance against a broad spectrum of pathogens in plants. Previous work indicates a role for plastidial glycerolipid biosynthesis in SAR. Specifically, mutations in FATTY ACID DESATURASE7 (FAD7), which lead to reduced trienoic fatty acid levels and compromised plastidial lipid biosynthesis, have been associated with defective SAR. We show that the defective SAR in Arabidopsis (Arabidopsis thaliana) fad7-1 plants is not associated with a mutation in FAD7 but rather with a second-site mutation in GLABRA1 (GL1), a gene well known for its role in trichome formation. The compromised SAR in gl1 plants is associated with impairment in their cuticles. Furthermore, mutations in two other components of trichome development, GL3 and TRANSPARENT TESTA GLABRA1, also impaired cuticle development and SAR. This suggests an overlap in the biochemical pathways leading to cuticle and trichome development. Interestingly, exogenous application of gibberellic acid (GA) not only enhanced SAR in wild-type plants but also restored SAR in gl1 plants. In contrast to GA, the defense phytohoromes salicylic acid and jasmonic acid were unable to restore SAR in gl1 plants. GA application increased levels of cuticular components but not trichome formation on gl1 plants, thus implicating cuticle, but not trichomes, as an important component of SAR. Our findings question the prudence of using mutant backgrounds for genetic screens and underscore a need to reevaluate phenotypes previously studied in the gl1 background.

Loss of Function of FATTY ACID DESATURASE7 in Tomato Enhances Basal Aphid Resistance in a Salicylate-Dependent Manner

“…Further work is needed to explore the potential interaction between NPR1 on fatty acid metabolism. Additional studies are also necessary to determine if aphid resistance in Arabidopsis FAD mutants is also SA dependent, particularly in light of recent conflicting reports about the potential impacts of FAD7 on SA signaling in this species (Chaturvedi et al, 2008;Xia et al, 2010). However, our findings are consistent with other studies indicating that SA can contribute to plant defenses against aphids in other tomato genotypes.…”

“…Potentially, increases in 9-hydroperoxyoctadecadienoic acid or other oxylipin derivatives of linoleic acid may contribute to aphid resistance in spr2. Alternatively, fatty acid desaturation could influence plant defenses against aphids by altering the composition of the plant's cuticle, which has recently been shown to play a role in defense signaling Xia et al, 2009Xia et al, , 2010.…”

Putative megaenzyme DWA1 plays essential roles in drought resistance by regulating stress-induced wax deposition in rice

“…FA extraction was performed as described by Xia et al (36). Wax extraction was conducted according to Lü et al (8) with minor modifications.…”

Apoplastic Diffusion Barriers in Arabidopsis

“…Changes in the ultrastructure and compositional analysis of the polyester in the cuticle revealed that LACS1 (At2g47249) and LACS2 are involved in cutin formation (Schnurr et al, 2004;Bessire et al, 2007;Lu et al, 2009;Weng et al, 2010). In addition, a mutation in LACS9 (At1g77590) leads to a permeable cuticle, indicating a role for the protein encoded by this gene in cutin formation (Xia et al, 2010). The characterization of the encoded proteins showed that these enzymes activate FAs of various chain lengths, including those present in cutin and suberin.…”