Banana production is seriously threatened by Fusarium wilt (FW), a disease caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc). In the mid-twentieth century FW, also known as "Panama disease", wiped out the Gros Michel banana industry in Central America. The devastation caused by Foc race 1 was mitigated by a shift to resistant Cavendish cultivars, which are currently the source of 99% of banana exports. However, a new strain of Foc, the tropical race 4 (TR4), attacks Cavendish clones and a diverse range of other banana varieties. Foc TR4 has been restricted to East and parts of Southeast Asia for more than 20 years, but since 2010 the disease has spread westward into five additional countries in Southeast and South Asia (Vietnam, Laos, Myanmar, India, and Pakistan) and at the transcontinental level into the Middle East (Oman, Jordan, Lebanon, and Israel) and Africa (Mozambique). The spread of Foc TR4 is of great concern due to the limited knowledge about key aspects of disease epidemiology and the lack of effective management models, including resistant varieties and soil management approaches. In this review we summarize the current knowledge on the epidemiology of FW of banana, highlighting knowledge gaps in pathogen survival and dispersal, factors driving disease intensity, soil and plant microbiome and the dynamics of the disease. Comparisons with FW in other crops were also made to indicate possible differences and commonalities. Our current understanding of the role of main biotic and abiotic factors on disease intensity is reviewed, highlighting research needs and futures directions. Finally, a set of practices and their impact on disease intensity are discussed and proposed as an integrative management approach that could eventually be used by a range of users, including plant protection organizations, researchers, extension workers and growers.

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Fusarium wilt of banana: Current knowledge on epidemiology and research needs toward sustainable disease management

The maize COMPACT PLANT2 locus encodes a Gα subunit; its interaction with leucine-rich receptors suggests a new mode of G-protein signalling that acts through single-pass rather than seven-pass G-protein-coupled transmembrane receptors. In plants the shoot apical meristem stem cells, responsible for stem growth, are maintained by a negative feedback loop between the CLAVATA signalling pathway and the WUSCHEL homeobox gene. In this study, David Jackson and colleagues demonstrate that in maize, the COMPACT PLANT2 (CT2) gene encodes a Gα subunit of a heterotrimeric GTP binding protein. CT2/Gα transmits a stem-cell-restrictive signal from a maize CLAVATA leucine-rich repeat receptor-like protein, FEA2, suggesting a previously unrecognized function for Gα signalling in plants. Single-pass transmembrane receptors act as G-protein coupled receptors (GPCRs) in plants, challenging the dogma that GPCRs are exclusively seven-transmembrane-domain receptor proteins. Shoot growth depends on meristems, pools of stem cells that are maintained by a negative feedback loop between the CLAVATA pathway and the WUSCHEL homeobox gene1. CLAVATA signalling involves a secreted peptide, CLAVATA3 (CLV3)2, and its perception by cell surface leucine-rich repeat (LRR) receptors, including the CLV1 receptor kinase3 and a LRR receptor-like protein, CLV2 (ref. 4). However, the signalling mechanisms downstream of these receptors are poorly understood, especially for LRR receptor-like proteins, which lack a signalling domain5. Here we show that maize COMPACT PLANT2 (CT2) encodes the predicted α-subunit (Gα) of a heterotrimeric GTP binding protein. Maize ct2 phenotypes resemble Arabidopsis thaliana clavata mutants, and genetic, biochemical and functional assays indicate that CT2/Gα transmits a stem-cell-restrictive signal from a CLAVATA LRR receptor, suggesting a new function for Gα signalling in plants. Heterotrimeric GTP-binding proteins are membrane-associated molecular switches that are commonly activated by ligand binding to an associated seven-pass transmembrane (7TM) G-protein-coupled receptor (GPCR)6. Recent studies have questioned the idea that plant heterotrimeric G proteins interact with canonical GPCRs7, and our findings suggest that single pass transmembrane receptors act as GPCRs in plants, challenging the dogma that GPCRs are exclusively 7TM proteins.

The maize Gα gene COMPACT PLANT2 functions in CLAVATA signalling to control shoot meristem size

https://escholarship.org/content/qt08z8r4ff/qt08z8r4ff.pdf?t=qa7nbx

101 Dothideomycetes genomes: A test case for predicting lifestyles and emergence of pathogens.

Nitrogen (N) is one of the most important elements that has a central impact on plant growth and yield. N is also widely involved in plant stress responses, but its roles in host-pathogen interactions are complex as each affects the other. In this review, we summarize the relationship between N nutrition and plant disease and stress its importance for both host and pathogen. From the perspective of the pathogen, we describe how N can affect the pathogen's infection strategy, whether necrotrophic or biotrophic. N can influence the deployment of virulence factors such as type III secretion systems in bacterial pathogen or contribute nutrients such as gamma-aminobutyric acid to the invader. Considering the host, the association between N nutrition and plant defence is considered in terms of physical, biochemical and genetic mechanisms. Generally, N has negative effects on physical defences and the production of anti-microbial phytoalexins but positive effects on defence-related enzymes and proteins to affect local defence as well as systemic resistance. N nutrition can also influence defence via amino acid metabolism and hormone production to affect downstream defence-related gene expression via transcriptional regulation and nitric oxide (NO) production, which represents a direct link with N. Although the critical role of N nutrition in plant defences is stressed in this review, further work is urgently needed to provide a comprehensive understanding of how opposing virulence and defence mechanisms are influenced by interacting networks.

https://www.mdpi.com/1422-0067/21/2/572/pdf

Unravelling the Roles of Nitrogen Nutrition in Plant Disease Defences.

Plant immunity: unravelling the complexity of plant responses to biotic stresses.

Moving nitrogen to the centre of plant defence against pathogens.

Non-symbiotic hemoglobin (nsHb) genes are ubiquitous in plants, but their biological functions have mostly been studied in model plant species rather than in crops. nsHb influences cell signaling and metabolism by modulating the levels of nitric oxide (NO). Class 1 nsHb is upregulated under hypoxia and is involved in various biotic and abiotic stress responses. Ectopic overexpression of nsHb in Arabidopsis thaliana accelerates development, whilst targeted overexpression in seeds can increase seed yield. Such observations suggest that manipulating nsHb could be a valid biotechnological target. We studied the effects of overexpression of class 1 nsHb in the monocotyledonous crop plant barley (Hordeum vulgare cv. Golden Promise). nsHb was shown to be involved in NO metabolism in barley, as ectopic overexpression reduced the amount of NO released during hypoxia. Further, as in Arabidopsis, nsHb overexpression compromised basal resistance toward pathogens in barley. However, unlike Arabidopsis, nsHb ectopic overexpression delayed growth and development in barley, and seed specific overexpression reduced seed yield. Thus, nsHb overexpression in barley does not seem to be an efficient strategy for increasing yield in cereal crops. These findings highlight the necessity for using actual crop plants rather than laboratory model plants when assessing the effects of biotechnological approaches to crop improvement.

An assessment of the biotechnological use of hemoglobin modulation in cereals.

The authors of this work are supported by a BBSRC Crop Science PhD studentship (to C.S.) a BBSRC-HGCA-DEFRA grant BB/I016910/1 (to L.A.J.M. and A.G.) and by AGL2010-15936 project from Spanish MEC (to E.P.).

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Catherine Simpson

Papers

Moving nitrogen to the centre of plant defence against pathogens.

An assessment of the biotechnological use of hemoglobin modulation in cereals.

Stomatal lock-up following pathogenic challenge: source or symptom of costs of resistance in crops?