Interspecies gene transfer provides soybean resistance to a fungal pathogen.

Fungal pathogens pose a major challenge to global crop production. Crop varieties that resist disease present the best defence and offer an alternative to chemical fungicides. Exploiting durable nonhost resistance (NHR) for crop protection often requires identification and transfer of NHR-linked genes to the target crop. Here, we identify genes associated with NHR of Arabidopsis thaliana to Phakopsora pachyrhizi, the causative agent of the devastating fungal disease called Asian soybean rust. We transfer selected Arabidopsis NHR-linked genes to the soybean host and discover enhanced resistance to rust disease in some transgenic soybean lines in the greenhouse. Interspecies NHR gene transfer thus presents a promising strategy for genetically engineered control of crop diseases.

ABC transporter PEN3/PDR8/ABCG36 interacts with calmodulin that, like PEN3, is required for Arabidopsis nonhost resistance.

Nonhost resistance (NHR) is the most prevalent form of plant immunity. In Arabidopsis, NHR requires membrane-localized ATP-binding cassette (ABC) transporter PENETRATION (PEN) 3. Upon perception of pathogen-associated molecular patterns, PEN3 becomes phosphorylated, suggestive of PEN3 regulation by post-translational modification. Here, we investigated the PEN3 protein interaction network. We probed the Arabidopsis protein microarray AtPMA-5000 with the N-terminal cytoplasmic domain of PEN3. Several of the proteins identified to interact with PEN3 in vitro represent cellular Ca(2+) sensors, including calmodulin (CaM) 3, CaM7 and several CaM-like proteins, pointing to the importance of Ca(2+) sensing to PEN3-mediated NHR. We demonstrated co-localization of PEN3 and CaM7, and we confirmed PEN3-CaM interaction in vitro and in vivo by PEN3 pull-down with CaM Sepharose, CaM overlay assay and bimolecular fluorescence complementation. We also show that just like in pen3, NHR to the nonadapted fungal pathogens Phakopsora pachyrhizi and Blumeria graminis f.sp. hordei is compromised in the Arabidopsis cam7 and pen3 cam7 mutants. Our study discloses CaM7 as a PEN3-interacting protein crucial to Arabidopsis NHR and emphasizes the importance of Ca(2+) sensing to plant immunity.

UDP-glucosyltransferase UGT84A2/BRT1 is required for Arabidopsis nonhost resistance to the Asian soybean rust pathogen Phakopsora pachyrhizi.

Nonhost resistance (NHR) of plants to fungal pathogens comprises different defense layers. Epidermal penetration resistance of Arabidopsis to Phakopsora pachyrhizi requires functional PEN1, PEN2 and PEN3 genes, whereas post-invasion resistance in the mesophyll depends on the combined functionality of PEN2, PAD4 and SAG101. Other genetic components of Arabidopsis post-invasion mesophyll resistance remain elusive. We performed comparative transcriptional profiling of wild-type, pen2 and pen2 pad4 sag101 mutants after inoculation with P. pachyrhizi to identify a novel trait for mesophyll NHR. Quantitative reverse transcription-polymerase chain reaction (RT-qPCR) analysis and microscopic analysis confirmed the essential role of the candidate gene in mesophyll NHR. UDP-glucosyltransferase UGT84A2/bright trichomes 1 (BRT1) is a novel component of Arabidopsis mesophyll NHR to P. pachyrhizi. BRT1 is a putative cytoplasmic enzyme in phenylpropanoid metabolism. BRT1 is specifically induced in pen2 with post-invasion resistance to P. pachyrhizi. Silencing or mutation of BRT1 increased haustoria formation in pen2 mesophyll. Yet, the brt1 mutation did not affect NHR to P. pachyrhizi in wild-type plants. We assign a novel function to BRT1, which is important for post-invasion NHR of Arabidopsis to P. pachyrhizi. BRT1 might serve to confer durable resistance against P. pachyrhizi to soybean.

Phakopsora pachyrhizi, the causal agent of Asian soybean rust.

UNLABELLED: The plant pathogenic basidiomycete fungi Phakopsora pachyrhizi and Phakopsora meibomiae cause rust disease in soybean plants. Phakopsora pachyrhizi originated in Asia-Australia, whereas the less aggressive P. meibomiae originated in Latin America. In the New World, P. pachyrhizi was first reported in the 1990s to have spread to Hawaii and, since 2001, it has been found in South America. In 2004, the pathogen entered continental USA. This review provides detailed information on the taxonomy and molecular biology of the pathogen, and summarizes strategies to combat the threat of this devastating disease. TAXONOMY: Phakopsora pachyrhizi Syd. & P. Syd; uredial anamorph: Malupa sojae (syn. Uredo sojae); Domain Eukaryota; Kingdom Fungi; Phylum Basidiomycota; Order Uredinales; Class Urediniomycetes; Family Phakopsoraceae; Genus Phakopsora (http://www.indexfungorum.org). The nomenclature of rust spores and spore-producing structures used within this review follows Agrios GN (2005) Plant Pathology, 5th edn. London: Elsevier/Academic Press. HOST RANGE: In the field, P. pachyrhizi infects leaf tissue from a broad range (at least 31 species in 17 genera) of leguminous plants. Infection of an additional 60 species in other genera has been achieved under laboratory conditions. DISEASE SYMPTOMS: At the beginning of the disease, small, tan-coloured lesions, restricted by leaf veins, can be observed on infected soybean leaves. Lesions enlarge and, 5-8 days after initial infection, rust pustules (uredia, syn. uredinia) become visible. Uredia develop more frequently in lesions on the lower surface of the leaf than on the upper surface. The uredia open with a round ostiole through which uredospores are released.

Characterization of nonhost resistance of Arabidopsis to the Asian soybean rust.

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is a devastating disease of soybean. We report the use of the nonhost plant Arabidopsis thaliana to identify the genetic basis of resistance to P. pachyrhizi. Upon attack by P. pachyrhizi, epidermal cells of wild-type Arabidopsis accumulated H2O2, which likely orchestrates the frequently observed epidermal cell death. However, even when epidermal cell death occurred, fungal hyphae grew on and infection was terminated at the mesophyll boundary. These events were associated with expression of PDF1.2, suggesting that P. pachyrhizi, an ostensible biotroph, mimics aspects of a necrotroph. Extensive colonization of the mesophyll occurred in Arabidopsis pen mutants with defective penetration resistance. Although haustoria were found occasionally in mesophyll cells, the successful establishment of biotrophy failed, as evidenced by the cessation of fungal growth. Double mutants affected in either jasmonic acid or salicylic acid signaling in the pen3-1 background revealed the involvement of both pathways in nonhost resistance (NHR) of Arabidopsis to P. pachyrhizi. Interestingly, expression of AtNHL10, a gene that is expressed in tissue undergoing the hypersensitive response, was only triggered in infected pen3-1 mutants. Thus, a suppression of P. pachyrhizi-derived effectors by PEN3 can be inferred. Our results demonstrate that Arabidopsis can be used to study mechanisms of NHR to ASR.