Arabidopsis ECERIFERUM9 Involvement in Cuticle Formation and Maintenance of Plant Water Status    

Abstract

Mutation of the ECERIFERUM9 (CER9) gene in Arabidopsis (Arabidopsis thaliana) causes elevated amounts of 18-carbon-length cutin monomers and a dramatic shift in the cuticular wax profile (especially on leaves) toward the very-long-chain free fatty acids tetracosanoic acid (C 24 ) and hexacosanoic acid (C 26 ). Relative to the wild type, cer9 mutants exhibit elevated cuticle membrane thickness over epidermal cells and cuticular ledges with increased occlusion of the stomatal pore. The cuticular phenotypes of cer9 are associated with delayed onset of wilting in plants experiencing water deficit, lower transpiration rates, and improved water use efficiency measured as carbon isotope discrimination. The CER9 protein thus encodes a novel determinant of plant drought tolerance-associated traits, one whose deficiency elevates cutin synthesis, redistributes wax composition, and suppresses transpiration. Map-based cloning identified CER9, and sequence analysis predicted that it encodes an E3 ubiquitin ligase homologous to yeast Doa10 (previously shown to target endoplasmic reticulum proteins for proteasomal degradation). To further elucidate CER9 function, the impact of CER9 deficiency on interactions with other genes was examined using double mutant and transcriptome analyses. For both wax and cutin, cer9 showed mostly additive effects with cer6, long-chain acyl-CoA synthetase1 (lacs1), and lacs2 and revealed its role in early steps of both wax and cutin synthetic pathways. Transcriptome analysis revealed that the cer9 mutation affected diverse cellular processes, with primary impact on genes associated with diverse stress responses. The discovery of CER9 lays new groundwork for developing novel cuticle-based strategies for improving the drought tolerance and water use efficiency of crop plants.Climatological drought is a historic problem for agriculture worldwide, as it limits crop production, and is now increasing as a threat due to climate change as well as dwindling ground and surface water resources. Genetic alterations that reduce overall transpirational water loss by crops are expected to conserve soil moisture and confer drought tolerance by delaying the onset of cellular dehydration stress during prolonged water deprivation (Nobel, 1999;Chaves et al., 2003;Kosma and Jenks, 2007). Stomata play a major role in regulating transpirational water loss through guard cell behavior (regulating stomatal aperture) and/or stomatal density over the leaf surface (Schroeder et al., 2001;Chaerle et al., 2005;Nilson and Assmann, 2007;Sirichandra et al., 2009;Kim et al., 2010). Transpiration is also controlled by the lipidic and hydrophobic plant cuticle, which coats the aerial surfaces of plants. The cuticle controls plant water loss associated with nonstomatal epidermal transpiration as well as transpiration through the stomatal pore via its role in forming the stomatal ledges (lips) and the cuticular coating that covers the mesophyll surfaces of the substomatal chamber (Xiao et al., 2004;Kerstiens, 2006;Kosma et al., 2009;L...

Leaf Development Monitoring and Early Detection of Water Deficiency by Low Field Nuclear Magnetic Resonance Relaxation in Nicotiana tabacum Plants

“…For these parameters, TIMAC SL28 was shown to be more effective in young and mature leaves than in old leaves. In addition, the DW of leaves sprayed with biostimulant was higher than that of control leaves at 57 DAS, which can be linked to adaptation to water stress, by, for example, increasing the cuticle [58] or trichome [59]. At harvest, the main benefit of applying the biostimulant was the concentration of N, which was equivalent to that in the control plants.…”

Improving Plant Water Use Efficiency through Molecular Genetics

“…Thus, genetic modification of OsGL1-6 may have great potential for improving the drought resistance of rice. Studies on mutation of the ECERIFERUM9 (CER9) gene in Arabidopsis showed a dramatic shift in the cuticular wax profile (especially on leaves) toward the very-long-chain free fatty acids tetracosanoic acid (C24) and hexacosanoic acid (C26) [101]. Compared with the wild type, cer9 mutants exhibit elevated cuticle membrane thickness over epidermal cells and cuticular ledges with increased occlusion of the stomatal pore.…”

Apoplastic Diffusion Barriers in Arabidopsis

“…Even plants that have significantly more wax and cutin than wt plants may exhibit increased cuticle permeability, indicating that the organization of cutin and wax is crucial in establishing a functional barrier at the leaf/atmosphere interface. However, a co-regulated increase of wax and cutin may indeed improve cuticular properties, as demonstrated by the cer9 Arabidopsis mutant (see above) (Lu et al, 2012).…”

“…In this context, the function of the CER9 protein, which is encoded by CER9 (At4g34100), a homologue of the E3 ubiquitin ligase DoA10 in yeast, which was previously demonstrated to target ER proteins for proteasomal degradation, is of great interest. Loss of CER9 activity leads to coordinated alterations in cutin and wax biosynthesis and improved sealing properties of the cuticle (Lu et al, 2012).…”