PMR5, an acetylation protein at the intersection of pectin biosynthesis and defense against fungal pathogens.

Powdery mildew (Golovinomyces cichoracearum), one of the most prolific obligate biotrophic fungal pathogens worldwide, infects its host by penetrating the plant cell wall without activating the plant's innate immune system. The Arabidopsis mutant powdery mildew resistant 5 (pmr5) carries a mutation in a putative pectin acetyltransferase gene that confers enhanced resistance to powdery mildew. Here, we show that heterologously expressed PMR5 protein transfers acetyl groups from [14 C]-acetyl-CoA to oligogalacturonides. Through site-directed mutagenesis, we show that three amino acids within a highly conserved esterase domain in putative PMR5 orthologs are necessary for PMR5 function. A suppressor screen of mutagenized pmr5 seed selecting for increased powdery mildew susceptibility identified two previously characterized genes affecting the acetylation of plant cell wall polysaccharides, RWA2 and TBR. The rwa2 and tbr mutants also suppress powdery mildew disease resistance in pmr6, a mutant defective in a putative pectate lyase gene. Cell wall analysis of pmr5 and pmr6, and their rwa2 and tbr suppressor mutants, demonstrates minor shifts in cellulose and pectin composition. In direct contrast to their increased powdery mildew resistance, both pmr5 and pmr6 plants are highly susceptibile to multiple strains of the generalist necrotroph Botrytis cinerea, and have decreased camalexin production upon infection with B. cinerea. These results illustrate that cell wall composition is intimately connected to fungal disease resistance and outline a potential route for engineering powdery mildew resistance into susceptible crop species.

Chiniquy D ，Underwood W ，Corwin J ，Ryan A ，Szemenyei H ，Lim CC ，Stonebloom SH ，Birdseye DS ，Vogel J ，Kliebenstein D ，Scheller HV ，Somerville S ... -  《-》

Mutations in PMR5 result in powdery mildew resistance and altered cell wall composition.

Vogel JP ，Raab TK ，Somerville CR ，Somerville SC ... -  《-》

Overexpression of a wheat stearoyl-ACP desaturase (SACPD) gene TaSSI2 in Arabidopsis ssi2 mutant compromise its resistance to powdery mildew.

Fatty acids and their derivatives play important roles in plant defense responses. It has been shown that a mutation in a gene encoding one of stearoyl acyl carrier protein fatty acid desaturase isoforms (ssi2 mutant) enhances the resistance of Arabidopsis to multiple pathogens, and similar results were obtained in rice and soybean. However, it is unknown whether the ssi2 mutant is also resistant to powdery mildew (Golovinomyces cichoracearum). In this study, the ssi2 mutant showed enhanced resistance to powdery mildew. Furthermore, we described the cloning and characterization of the TaSSI2 gene (ortholog of AtSSI2) from wheat. Functional analysis of TaSSI2 was performed by overexpressing TaSSI2 in ssi2 mutant of Arabidopsis. The result indicated that ectopic expression of TaSSI2 restored the WT like morphology in the ssi2 background, the 35S:TaSSI2/ssi2 plants accumulated WT-like levels of oleic acid (18:1) and the transcript levels of R genes were significantly lower than that in ssi2 plants. In contrast to the constitutive PR gene expression in ssi2 plants, the transcript accumulation of PR1 and PR2 was similar in the 35S:TaSSI2/ssi2 and wild type both before and after inoculation. Trypan blue staining showed that extensive fungal hyphae and conidiophores were produced in wild-type and 35S:TaSSI2/ssi2 leaves while no visible powdery mildew growth was observed, but dramatic lesions developed at the infection sites in the ssi2 mutant leaves. Our results demonstrated that TaSSI2 is involved in the negative regulation of defense responses in powdery mildew infection, similar to its counterparts in Arabidopsis, indicating a highly conserved function of SSI2 gene in diverse plants.

Song N ，Hu Z ，Li Y ，Li C ，Peng F ，Yao Y ，Peng H ，Ni Z ，Xie C ，Sun Q ... -  《-》

PMR6, a pectate lyase-like gene required for powdery mildew susceptibility in Arabidopsis.

Vogel JP ，Raab TK ，Schiff C ，Somerville SC ... -  《-》

A mutation in a coproporphyrinogen III oxidase gene confers growth inhibition, enhanced powdery mildew resistance and powdery mildew-induced cell death in Arabidopsis.

Guo CY ，Wu GH ，Xing J ，Li WQ ，Tang DZ ，Cui BM ... -  《-》