Proceedings of the COST SUSVAR/ECO-PB Workshop on organic plant breeding strategies and the use of molecular markers

In many countries,national projects are in progress to investigate the sustainable low-input approach.In the present COST network,these projects are coordinated by means of exchange of materials,establishing common methods for assessment and statistical analyses and by combining national experimental results.The common framework is cereal production in low-input sustainable systems with emphasis on crop diversity.The network is organised into six Working Groups,five focusing on specific research areas and one focusing on the practical application of the research results for variety testing:1)plant genetics and plant breeding,2)biostatistics,3)plant nutrition and soil microbiology,4)weed biology and plant competition,5)plant pathology and plant disease resistance biology and 6)variety testing and certification.It is essential that scientists from many disciplines work together to investigate the complex interactions between the crop and its environment,in order to be able to exploit the natural regulatory mechanisms of different agricultural systems for stabilising and increasing yield and quality.The results of this cooperation will contribute to commercial plant breeding as well as official variety testing,when participants from these areas disperse the knowledge achieved through the EU COST Action

Non-structural proteins of arthropod-borne bunyaviruses: roles and functions

Viruses within the Bunyaviridae family are tri-segmented, negative-stranded RNA viruses. The family includes several emerging and re-emerging viruses of humans, animals and plants, such as Rift Valley fever virus, Crimean-Congo hemorrhagic fever virus, La Crosse virus, Schmallenberg virus and tomato spotted wilt virus. Many bunyaviruses are arthropod-borne, so-called arboviruses. Depending on the genus, bunyaviruses encode, in addition to the RNA-dependent RNA polymerase and the different structural proteins, one or several non-structural proteins. These non-structural proteins are not always essential for virus growth and replication but can play an important role in viral pathogenesis through their interaction with the host innate immune system. In this review, we will summarize current knowledge and understanding of insect-borne bunyavirus non-structural protein function(s) in vertebrate, plant and arthropod

Leaf Eh and pH: A Novel Indicator of Plant Stress. Spatial, Temporal and Genotypic Variability in Rice (Oryza sativa L.)

A wealth of knowledge has been published in the last decade on redox regulations in plants. However, these works remained largely at cellular and organelle levels. Simple indicators of oxidative stress at the plant level are still missing. We developed a method for direct measurement of leaf Eh and pH, which revealed spatial, temporal, and genotypic variations in rice. Eh (redox potential) and Eh@pH7 (redox potential corrected to pH 7) of the last fully expanded leaf decreased after sunrise. Leaf Eh was high in the youngest leaf and in the oldest leaves, and minimum for the last fully expanded leaf. Leaf pH decreased from youngest to oldest leaves. The same gradients in Eh-pH were measured for various varieties, hydric conditions, and cropping seasons. Rice varieties differed in Eh, pH, and/or Eh@pH7. Leaf Eh increases and leaf pH decreases with plant age. These patterns and dynamics in leaf Eh-pH are in accordance with the pattern and dynamics of disease infections. Leaf Eh-pH can bring new insight on redox processes at plant level and is proposed as a novel indicator of plant stress/health. It could be used by agronomists, breeders, and pathologists to accelerate the development of crop cultivation methods leading to agroecological crop protection

Transgenic resistance to PMTV and PVA provides novel insights to viral long-distance movement

The studies in this thesis describe forms of transgenic resistance to plant viruses and how they can be used for studying viral infection cycle. S. tuberosum cv. Saturna expressing the CP gene of Potato mop-top virus (PMTV) was grown in a field infested with the viruliferous vector of PMTV, S. subterranea. The incidence of PMTV-infected tubers was lower in the CP-transgenic potato than in non-transgenic potato. RNA dot-blot analysis revealed that in tubers infected with PMTV, all three RNAs were present. N. benthamiana plants expressing the CP gene of PMTV were inoculated by two different methods i) mechanical inoculation to leaves and ii) growing plants in soil infested with viruliferous S. subterranea. Results showed that the expression of the transgene-derived RNA (or CP) inhibits replication of homologous RNA 2 in transgenic N. benthamiana. Furthermore, the results showed that transgene-mediated resistance to PMTV differs in roots and leaves. Mechanical inoculation with PMTV on CP-transgenic N. benthamiana resulted in symptomless, systemic movement of RNA 1 and RNA 3, but not the CP-encoding RNA (RNA 2). These findings show that PMTV RNA 1 and RNA 3 can infect and move systemically in N. benthamiana without the CP and RNA 2. N. benthamiana transformed with the P1 and VPg cistron, respectively, of Potato virus A (PVA) displayed: i) resistance to PVA infection, ii) susceptibility, or iii) systemic infection followed by recovery from PVA infection of new leaves. Long-distance transport of PVA from lower, infected parts of recovered plants was compromised in the recovered tissue. This result suggests that PVA is moving as ribonucleoprotein complex other than virus particles. N. benthamiana transformed with a polycistronic transgene encoding the CI-NIa-CP cistrons of PVA was susceptible to PVA infection. VPg (the N-proximal part of NIa) is a well-known virulence factor of potyviruses and its possible role in suppression of RNA silencing was studied. PVA VPg was found to increase the severity of disease symptoms when expressed from a Potato virus X vector in N. benthamiana. However, PVA VPg did not show apparent RNA silencing suppression activity. The reason why the polycistronic transgene did not provide resistance could not be resolved

Differences in microbiota between two multilocus lineages of the sugarcane Aphid (Melanaphis sacchari) in the continental United States

The sugarcane aphid (SCA), Melanaphis Sacchari (Zehntner) (Hemiptera: Aphididae), has been considered an invasive pest of sugarcane in the continental United States since 1977. Then, in 2013, SCA abruptly became a serious pest of U.S. sorghum and is now a sorghum pest in 22 states across the continental United States. Changes in insect-associated microbial community composition are known to influence host-plant range in aphids. In this study, we assessed whether changes in microbiota composition may explain the SCA outbreak in U.S. sorghum. We characterized the SCA bacterial microbiota on sugarcane and grain sorghum in four U.S. states, using a metabarcoding approach. In addition, we used taxon-specific polymerase chain reaction (PCR) primers to screen for bacteria commonly reported in aphid species. As anticipated, all SCA harbored the primary aphid endosymbiont Buchnera aphidicola, an obligate mutualistic bacterial symbiont. Interestingly, none of the secondary symbionts, facultative bacteria typically associated with aphids (e.g., Arsenophonus, Hamiltonella, Regiella) were present in either the metabarcoding data or PCR screens (with the exception of Rickettsiella and Serratia, which were detected by metabarcoding at low abundances <1%). However, our metabarcoding detected bacteria not previously identified in aphids (Arcobacter, Bifidobacterium, Citrobacter). Lastly, we found microbial host-associated differentiation in aphids that seems to correspond to genetically distinct aphid lineages that prefer to feed on grain sorghum (MLL-F) versus sugarcane (MLL-D)

A wheat caffeic acid 3-O-methyltransferase TaCOMT-3D positively contributes to both resistance to sharp eyespot disease and stem mechanical strength

Plant caffeic acid 3-O-methyltransferase (COMT) has been implicated in the lignin biosynthetic pathway through catalyzing the multi-step methylation reactions of hydroxylated monomeric lignin precursors. However, genetic evidence for its function in plant disease resistance is poor. Sharp eyespot, caused primarily by the necrotrophic fungus Rhizoctonia cerealis, is a destructive disease in hexaploid wheat (Triticum aestivum L.). In this study, a wheat COMT gene TaCOMT-3D, is identified to be in response to R. cerealis infection through microarray-based comparative transcriptomics. The TaCOMT-3D gene is localized in the long arm of the chromosome 3D. The transcriptional level of TaCOMT-3D is higher in sharp eyespot-resistant wheat lines than in susceptible wheat lines, and is significantly elevated after R. cerealis inoculation. After R. cerealis inoculation and disease scoring, TaCOMT-3D-silenced wheat plants exhibit greater susceptibility to sharp eyespot compared to unsilenced wheat plants, whereas overexpression of TaCOMT-3D enhances resistance of the transgenic wheat lines to sharp eyespot. Moreover, overexpression of TaCOMT-3D enhances the stem mechanical strength, and lignin (particular syringyl monolignol) accumulation in the transgenic wheat lines. These results suggest that TaCOMT-3D positively contributes to both wheat resistance against sharp eyespot and stem mechanical strength possibly through promoting lignin (especially syringyl monolignol) accumulation

e-Book on plant virus infection—a cell biology perspective

International audiencePas de résum

Jasmonate-induced defense mechanisms in the belowground antagonistic interaction between Pythium arrhenomanes and Meloidogyne graminicola in rice

Next to their essential roles in plant growth and development, phytohormones play a central role in plant immunity against pathogens. In this study we studied the previously reported antagonism between the plant-pathogenic oomycete Pythium arrhenomanes and the root-knot nematode Meloidogyne graminicola, two root pathogens that co-occur in aerobic rice fields. In this manuscript, we investigated if the antagonism is related to imbalances in plant hormone levels, which could be involved in activation of plant defense. Hormone measurements and gene expression analyses showed that the jasmonate (JA) pathway is induced early upon P. arrhenomanes infection. Exogenous application of methyl-jasmonate (MeJA) on the plant confirmed that JA is needed for basal defense against both P. arrhenomanes and M. graminicola in rice. Whereas M. graminicola suppresses root JA levels to increase host susceptibility, Pythium inoculation boosts JA in a manner that prohibits JA repression by the nematode in double-inoculated plants. Exogenous MeJA supply phenocopied the defense-inducing capacity of Pythium against the root-knot nematode, whereas the antagonism was weakened in JA-insensitive mutants. Transcriptome analysis confirmed upregulation of JA biosynthesis and signaling genes upon P. arrhenomanes infection, and additionally revealed induction of genes involved in biosynthesis of diterpenoid phytoalexins, consistent with strong activation of the gene encoding the JA-inducible transcriptional regulator DITERPENOID PHYTOALEXIN FACTOR. Altogether, the here-reported data indicate an important role for JA-induced defense mechanisms in this antagonistic interaction. Next to that, our results provide evidence for induced expression of genes encoding ERF83, and related PR proteins, as well as auxin depletion in P. arrhenomanes infected rice roots, which potentially further contribute to the reduced nematode susceptibility seen in double-infected plants

Next-Generation Sequencing and Genome Editing in Plant Virology

Next-generation sequencing (NGS) has been applied to plant virology since 2009. NGS provides highly efficient, rapid, low cost DNA, or RNA high-throughput sequencing of the genomes of plant viruses and viroids and of the specific small RNAs generated during the infection process. These small RNAs, which cover frequently the whole genome of the infectious agent, are 21–24 nt long and are known as vsRNAs for viruses and vd-sRNAs for viroids. NGS has been used in a number of studies in plant virology including, but not limited to, discovery of novel viruses and viroids as well as detection and identification of those pathogens already known, analysis of genome diversity and evolution, and study of pathogen epidemiology. The genome engineering editing method, clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system has been successfully used recently to engineer resistance to DNA geminiviruses (family, Geminiviridae) by targeting different viral genome sequences in infected Nicotiana benthamiana or Arabidopsis plants. The DNA viruses targeted include tomato yellow leaf curl virus and merremia mosaic virus (begomovirus); beet curly top virus and beet severe curly top virus (curtovirus); and bean yellow dwarf virus (mastrevirus). The technique has also been used against the RNA viruses zucchini yellow mosaic virus, papaya ringspot virus and turnip mosaic virus (potyvirus) and cucumber vein yellowing virus (ipomovirus, family, Potyviridae) by targeting the translation initiation genes eIF4E in cucumber or Arabidopsis plants. From these recent advances of major importance, it is expected that NGS and CRISPR-Cas technologies will play a significant role in the very near future in advancing the field of plant virology and connecting it with other related fields of biology.Work in RF laboratory has been supported by the Spanish Ministerio de Economía y Competitividad (grant BFU2014-56812-P), and in MB laboratory by Consiglio per la Ricerca in Agricoltura e l’analisi dell’Economia Agraria (CREA).Peer reviewedPeer Reviewe