The plant cuticle is a chemically heterogeneous lipophilic layer composed of a cutin polymer matrix and waxes which covers the aerial parts of plants. This layer plays an essential role in the survival of plants by protecting them from desiccation and (a)biotic stresses. Knowledge on the gene networks and mechanisms regulating the synthesis of cuticle components during organ expansion or stress response remains limited however. Here, using five loss-of-function mutants for histone monoubiquitination, we report on the role of two RING E3 ligases, namely HISTONE MONOUBIQUITINATION 1 and 2 (HUB1 and HUB2), in the selective transcriptional activation of four cuticle biosynthesis genes in Arabidopsis thaliana. Microscopy observations showed that in hub1-6 and hub2-2 mutants irregular epidermal cells and disorganized cuticle layers were present in rosette leaves. Water loss measurements on excised rosettes demonstrated that cuticular permeability was significantly increased in the mutants. Chemical analysis of cuticle components revealed that the wax composition was changed and that cutin 16:0 dicarboxylic acid was significantly reduced in all hub mutants. Analysis of transcript levels of selected genes indicated that LACS2, ATT1 and HOTHEAD involved in cutin biosynthesis and CER1 involved in wax biosynthesis were down-regulated in the hub mutants, while the expression of LACERATA, CER3, CER6 and CER10 remained unchanged. Chromatin immunoprecipitation assays further showed that hub mutants are impaired in dynamic changes of histone H2B monoubiquitination at several loci of down-regulated genes. Taken together, these data establish that the regulation of cuticle composition involves chromatin remodeling by H2B monoubiquitination.

Septoria tritici blotch caused by the fungus Zymoseptoria tritici is one of the most devastating foliar diseases of wheat. Knowledge regarding mechanisms involved in resistance against this disease is required to breed durable resistances. This study compared the expression of defence and pathogenicity determinants in three cultivars in semicontrolled culture conditions. The most susceptible cultivar, Alixan, presented higher necrosis and pycnidia density levels than Altigo, the most resistant one. In Premio, a moderately resistant cultivar, necrosis developed as in Alixan, while pycnidia developed as in Altigo. In noninfectious conditions, genes coding for PR1 (pr1), glucanase (gluc) and allene oxide synthase (aos) were constitutively expressed at a higher level in both Altigo and Premio than in Alixan, while chitinase2 (chit2), phenylalanine ammonia-lyase (pal), peroxidase (pox2) and oxalate oxidase (oxo) were expressed at a higher level in Premio only. Except for aos, all genes were induced in Alixan during the first steps of the symptomless infection phase. Only pox2, oxo, gluc and pal genes in Altigo and pal, chs and lox genes in Premio were up-regulated at some time points. Basal cultivar-dependent resistance against Z. tritici could therefore be explained by various gene expression patterns rather than high expression levels of given genes. During the necrotrophic phase, Z. tritici cell wall-degrading enzyme activity levels were lower in Altigo and Premio than in Alixan, and were associated more with pycnidia than with necrosis. Similar tissue colonization occurred in the three cultivars, suggesting an inhibition of the switch to the necrotrophic lifestyle in Altigo.

The induction of plant defense mechanisms by resistance inducers is an attractive and innovative alternative to reduce the use of fungicides on wheat against Zymoseptoria tritici, the responsible agent of Septoria tritici blotch (STB). Under controlled conditions, we investigated the resistance induction in three wheat cultivars with different susceptible levels to STB as a response to a treatment with a sulfur, manganese sulfate, and protein-based resistance inducer (NECTAR Céréales). While no direct antigermination effect of the product was observed in planta, more than 50% reduction of both symptoms and sporulation were recorded on the three tested cultivars. However, an impact of the wheat genotype on resistance induction was highlighted, which affects host penetration, cell colonization, and the production of cell-wall degrading enzymes by the fungus. Moreover, in the most susceptible cultivar Alixan, the product upregulated POX2, PAL, PR1, and GLUC gene expression in both noninoculated and inoculated plants and CHIT2 in noninoculated plants only. In contrast, defense responses induced in Altigo, the most resistant cultivar, seem to be more specifically mediated by the phenylpropanoid pathway in noninoculated as well as inoculated plants, since PAL and CHS were most specifically upregulated in this cultivar. In Premio, the moderate resistant cultivar, NECTAR Céréales elicits mainly the octadecanoid pathway, via LOX and AOS induction in noninoculated plants. We concluded that this complex resistance-inducing product protects wheat against Z. tritici by stimulating the cultivar-dependent plant defense mechanisms.