An overview of genetic rust resistance: From broad to specific mechanisms

Global agriculture is under threat due to the rapid evolution and spread of pathogenic fungi that cause rust diseases. For instance, the recently evolved races of wheat stem rust (Puccinia graminis f. sp. tritici) and stripe rust (P. striiformis f. sp. tritici) fungus in parts of Africa, Asia, and Europe are a menace to food security due to their ability to spread rapidly and overcome resistance in common wheat varieties [1]. Similarly, new variants of Asian soybean rust (Phakopsora pachyrhizi) detected in Brazil and the United States pose a major constraint to soybean cultivation [2]. Since genetic resistance can provide effective and chemical-free disease control, many efforts are directed towards isolating rust-resistance genes in crop plants and understanding how to best deploy them for durable resistance [3]. In addition, related nonhost species are increasingly being utilised to identify new sources of resistance [4, 5]. Here, we summarise current knowledge of rust resistance, focussing on race-specific, non–race-specific, and nonhost resistance mechanisms.Work in the authors’ laboratory is supported by the Grains Research and Development Corporation (https://grdc.com.au/) grant # CSP0016

Are sucrose transporter expression profiles linked with patterns of biomass partitioning in Sorghum phenotypes?

Sorghum bicolor is a genetically diverse C4 monocotyledonous species, encompassing varieties capable of producing high grain yields as well as sweet types which accumulate soluble sugars (predominantly sucrose) within their stems to high concentrations. Sucrose produced in leaves (sources) enters the phloem and is transported to regions of growth and storage (sinks). It is likely that sucrose transporter (SUT) proteins play pivotal roles in phloem loading and the delivery of sucrose to growth and storage sinks in all Sorghum ecotypes. Six SUTs are present in the published Sorghum genome, based on the BTx623 grain cultivar. Homologues of these SUTs were cloned and sequenced from the sweet cultivar Rio, and compared with the publically available genome information. SbSUT5 possessed nine amino acid sequence differences between the two varieties. Two of the remaining five SUTs exhibited single variations in their amino acid sequences (SbSUT1 and SbSUT2) whilst the rest shared identical sequences. Complementation of a mutant Saccharomyces yeast strain (SEY6210), unable to grow up on sucrose as the sole carbon source, demonstrated that the Sorghum SUTs were capable of transporting sucrose. SbSUT1, SbSUT4, and SbSUT6 were highly expressed in mature leaf tissues and hence may contribute to phloem loading. In contrast, SbSUT2 and SbSUT5 were expressed most strongly in sinks consistent with a possible role of facilitating sucrose import into stem storage pools and developing inflorescences.Ricky J. Milne, Caitlin S. Byrt, John W. Patrick and Christopher P. L. Gro

The wheat Lr34 multi-pathogen resistance gene confers resistance to anthracnose and rust in sorghum

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Epigenetic regulator genes direct lineage switching in MLL/AF4 leukaemia

The fusion gene MLL/AF4 defines a high-risk subtype of pro-B acute lymphoblastic leukaemia. Relapse can be associated with a lineage switch from acute lymphoblastic to acute myeloid leukaemia resulting in poor clinical outcomes due to resistance towards chemo- and immuno-therapies. Here we show that the myeloid relapses share oncogene fusion breakpoints with their matched lymphoid presentations and can originate from varying differentiation stages from immature progenitors through to committed B-cell precursors. Lineage switching is linked to substantial changes in chromatin accessibility and rewiring of transcriptional programmes, including alternative splicing. These findings indicate that the execution and maintenance of lymphoid lineage differentiation is impaired. The relapsed myeloid phenotype is recurrently associated with the altered expression, splicing or mutation of chromatin modifiers, including CHD4 coding for the ATPase/helicase of the nucleosome remodelling and deacetylation complex, NuRD. Perturbation of CHD4 alone or in combination with other mutated epigenetic modifiers induces myeloid gene expression in MLL/AF4-positive cell models indicating that lineage switching in MLL/AF4 leukaemia is driven and maintained by disrupted epigenetic regulation

Effectiveness of a national quality improvement programme to improve survival after emergency abdominal surgery (EPOCH): a stepped-wedge cluster-randomised trial

Background: Emergency abdominal surgery is associated with poor patient outcomes. We studied the effectiveness of a national quality improvement (QI) programme to implement a care pathway to improve survival for these patients. Methods: We did a stepped-wedge cluster-randomised trial of patients aged 40 years or older undergoing emergency open major abdominal surgery. Eligible UK National Health Service (NHS) hospitals (those that had an emergency general surgical service, a substantial volume of emergency abdominal surgery cases, and contributed data to the National Emergency Laparotomy Audit) were organised into 15 geographical clusters and commenced the QI programme in a random order, based on a computer-generated random sequence, over an 85-week period with one geographical cluster commencing the intervention every 5 weeks from the second to the 16th time period. Patients were masked to the study group, but it was not possible to mask hospital staff or investigators. The primary outcome measure was mortality within 90 days of surgery. Analyses were done on an intention-to-treat basis. This study is registered with the ISRCTN registry, number ISRCTN80682973. Findings: Treatment took place between March 3, 2014, and Oct 19, 2015. 22 754 patients were assessed for elegibility. Of 15 873 eligible patients from 93 NHS hospitals, primary outcome data were analysed for 8482 patients in the usual care group and 7374 in the QI group. Eight patients in the usual care group and nine patients in the QI group were not included in the analysis because of missing primary outcome data. The primary outcome of 90-day mortality occurred in 1210 (16%) patients in the QI group compared with 1393 (16%) patients in the usual care group (HR 1·11, 0·96–1·28). Interpretation: No survival benefit was observed from this QI programme to implement a care pathway for patients undergoing emergency abdominal surgery. Future QI programmes should ensure that teams have both the time and resources needed to improve patient care. Funding: National Institute for Health Research Health Services and Delivery Research Programme

Effectiveness of a national quality improvement programme to improve survival after emergency abdominal surgery (EPOCH): a stepped-wedge cluster-randomised trial

BACKGROUND: Emergency abdominal surgery is associated with poor patient outcomes. We studied the effectiveness of a national quality improvement (QI) programme to implement a care pathway to improve survival for these patients. METHODS: We did a stepped-wedge cluster-randomised trial of patients aged 40 years or older undergoing emergency open major abdominal surgery. Eligible UK National Health Service (NHS) hospitals (those that had an emergency general surgical service, a substantial volume of emergency abdominal surgery cases, and contributed data to the National Emergency Laparotomy Audit) were organised into 15 geographical clusters and commenced the QI programme in a random order, based on a computer-generated random sequence, over an 85-week period with one geographical cluster commencing the intervention every 5 weeks from the second to the 16th time period. Patients were masked to the study group, but it was not possible to mask hospital staff or investigators. The primary outcome measure was mortality within 90 days of surgery. Analyses were done on an intention-to-treat basis. This study is registered with the ISRCTN registry, number ISRCTN80682973. FINDINGS: Treatment took place between March 3, 2014, and Oct 19, 2015. 22 754 patients were assessed for elegibility. Of 15 873 eligible patients from 93 NHS hospitals, primary outcome data were analysed for 8482 patients in the usual care group and 7374 in the QI group. Eight patients in the usual care group and nine patients in the QI group were not included in the analysis because of missing primary outcome data. The primary outcome of 90-day mortality occurred in 1210 (16%) patients in the QI group compared with 1393 (16%) patients in the usual care group (HR 1·11, 0·96-1·28). INTERPRETATION: No survival benefit was observed from this QI programme to implement a care pathway for patients undergoing emergency abdominal surgery. Future QI programmes should ensure that teams have both the time and resources needed to improve patient care. FUNDING: National Institute for Health Research Health Services and Delivery Research Programme

Phloem loading and unloading pathways in sorghum bicolor: the role of sucrose transporters in export and storage of sucrose

Research Doctorate - Doctor of Philosophy (PhD)Stem sucrose accumulation within C4 monocotyledonous plant species is of both commercial and biological interest. Although mechanisms underlying stem sucrose accumulation are not well understood, it is likely that sucrose transporters (SUTs) play an important role in delivery of sucrose to stem sinks. Sorghum bicolor is an ideal monocotyledonous model for investigating SUTs, as this species can store sucrose within its stem to high concentrations (exceeding 500 mM). Further, the full genomic sequence is publicly available. Sucrose produced in photosynthesising leaves (source tissues) enters the phloem and is transported to regions of growth and storage (sink tissues). This source-sink pathway of sucrose transport in sweet Sorghum was investigated using histochemical stains and tracer dyes. The involvement of SUTs in phloem loading and unloading was also investigated by expression, localisation and functional characterisation studies. Cell to cell transport of sucrose can occur via plasmodesmal connections (symplasmic) or via the apoplasm with transporters mediating sucrose passage across plasma membranes (apoplasmic). Deposition of lignin and suberin is associated with vascular bundles, especially in stems. These complex polymers deposited in the apoplasmic space can restrict apoplasmic solute movement. In the Sorghum source leaf, minimal lignification and suberisation was observed. At the predicted site of phloem loading, small vascular bundles, lignin and suberin were primarily deposited in bundle sheath cell walls interfacing with mesophyll cells. The apoplasmic tracer dye, PTS was unable to pass through these lignified and suberised bundle sheaths. The symplasmic tracer dye, CF (loaded as CFDA) was restricted in sieve elements (SEs). This indicated that sucrose may follow a symplasmic path through the bundle sheath, before it is released to the apoplasm and actively transported into sieve element-companion cell (SE-CC) complexes. This sucrose is then exported to sinks through the long distance transport pathway. Lignin was present in walls of protoxylem elements of meristematic, elongating and recently elongated internodal zones. Suberin was absent from these zones. Because of this, the apoplasmic tracer, PTS was unrestricted between SE and storage parenchyma apoplasms. In maturing and mature internodal zones, heavy lignification and suberisation of sclerenchyma sheath cell walls restricted apoplasmic tracer movement between SE and storage parenchyma apoplasms. Hence symplasmic unloading was required for sucrose to pass the lignified and suberised sclerenchyma sheath. Symplasmic continuity between SEs and storage parenchyma cells was comfirmed by PTS as a symplasmic tracer dye (loaded as PTSA). These observations were used to investigate the function of sucrose transporters in loading and unloading. Six sucrose transporters were identified in the Sorghum genomic sequence and cloned from low and high sugar accumulating cultivars – a grain cultivar (BTx623) and a sweet cultivar (Rio). The SUTs were cloned and transformed into the mutant SEY6210 strain of Saccharomyces cerevisiae (not capable of using sucrose as a carbon source) and confirmed as sucrose transport capable by complementation on solid media. Additionally, a variant of SUT5 was identified in a sweet cultivar, Rio, which possessed nine amino acid differences to the SUT5 from cv. BTx623, and was also transport functional. Transporter expression in yeast and oocytes revealed that SbSUT1 and SbSUT5 were sucrose transport capable in both, and additionally SbSUT5G (SUT5 from grain Sorghum cultivar, BTx623) was sucrose transport capable in oocytes. SbSUT4 was found to be non-functional in yeast or oocytes as it was not localised to the plasma membrane. SbSUT1 and SbSUT5 were dependent on a proton gradient as treatment by the protonophores, 2,4-DNP and CCCP resulted in a reduction in sucrose uptake in yeast. SbSUT1 and SbSUT5 were also found to be DEPC sensitive and possessed a conserved histidine residue. All three SUTs were dependent on the proton motive force (pmf) and both components (pH and membrane potential) affected sucrose transport into oocytes. All were highly selective for sucrose and affinities were similar to other monocot SUTs. Three SbSUTs were expressed strongly in source leaves (SbSUT1, SbSUT4, SbSUT6). SbSUT4 localised to the tonoplast of tobacco leaf protoplasts and was immunolocalised to Sorghum mesophyll cells. SbSUT4 is likely to buffer cytosolic sucrose levels for phloem loading. Supporting apoplasmic loading in Sorghum, sucrose transporters were immunolocalised with the generic PEP2 antiserum to SE plasma membranes in source leaf minor veins. SbSUT1, localised to the plasma membrane of tobacco leaf protoplasts, may load sucrose into sieve elements of small vascular bundles. SbSUT1 demonstrated high affinity and selectivity for sucrose, supporting a phloem loading function. SbSUT6 is predicted to have a similar function. Unloading from protophloem SEs in meristematic and elongating zones of the internode was predicted to be apoplasmic, due to symplasmic isolation of protophloem SEs in other species. SbSUTs were immunolocalised to SEs and are likely to function in sucrose retrieval. Low expression observed in developing zones may indicate low levels of retrieval by SbSUT2 and SbSUT5, hence unloading to the vein apoplasm may occur by diffusion. Sucrose may be cleaved by cell wall invertase and loaded into parenchyma cells by hexose transporters. Alternatively, SUTs localised to the plasma membrane of parenchyma cells may load sucrose into these cells. In maturing internode zones, radial sucrose transport was via a symplasmic route. SbSUT1 was highly expressed, and SbSUTs were localised by generic antiserum (PEP2) to SE-CC and storage parenchyma plasma membranes. These SUTs are likely to function in sucrose retrieval, in order to maintain turgor homeostasis to support unloading to storage parenchyma cells by bulk flow. Preferential expression of the tonoplast antiporters SbTMT1 and SbTMT2 in zones actively accumulating sucrose suggests they may function to mediate sucrose entry into vacuoles. Overall, work presented in this thesis extends the limited understanding of source to sink transport in monocotyledonous species which accumulate sucrose. Sucrose transporters were found to be directly involved in phloem loading, and they are likely to be associated with phloem unloading in different capacities across developmental stages

Host and nonhost mechanisms of rust resistance.

<p>Race-specific and non–race-specific resistances can be phenotypically quite different (A versus B). <b>(A)</b> Strong resistance is conferred by NLR proteins such as stem rust resistance 45 (Sr45) and is associated with a hypersensitive response. <b>(B)</b> Non–race-specific resistance may be characterised by partial resistance or slowed fungal growth coupled to leaf-tip necrosis in the presence of genes such as <i>leaf rust resistance 67</i> (<i>Lr67</i>). <b>(C)</b> Adapted pathogens deliver effectors that can subvert pathogen-associated molecular patterns (PAMP)-triggered immunity (PTI), but which may be detected in the plant cell by nucleotide-binding and leucine-rich repeat (NLR) proteins, leading to effector-triggered immunity (ETI). <b>(D)</b> PTI can operate in nonhost resistance in response to nonadapted pathogens, and ETI can also occur for pathogens that are more compatible to the host plant. <i>R</i>-gene capture methods may be used to detect and identify <i>NLR</i> genes, with the goal of incorporation of these <i>NLR</i>s into <i>R</i>-gene cassettes or stacks to provide durable, long-lasting resistance.</p