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Effect on tomato plants of asymptomatic infection with southern tomato virus

ABSTRACT: Southern tomato virus (STV) often infects healthy tomato plants (Solanum lycopersicum). In this study, we compared STV-free and STV-infected cultivar M82 plants to determine the effect of STV infection on the host plant. STV-free plants exhibited a short and bushy phenotype, whereas STV-infected plants exhibited increased height. STV-infected plants produced more fruit than STV-free plants, and the germination rate of seeds from STV-infected plants was higher than that of seeds from STV-free plants. This phenotypic difference was also observed in progeny plants (siblings) derived from a single STV-infected plant in which the transmission rate of STV to progeny plants via the seeds was approximately 86%. These results suggest that the interaction between STV and host plants is mutualistic. Transcriptome analyses revealed that STV infection affected gene expressions in host plants, notably evidenced by down-regulation of genes involved in ethylene biosynthesis and signaling. STV-infected tomato plants thus might be artificially selected due to their superior traits as a crop.

ORGANISM(S): Solanum lycopersicum

PROVIDER: GSE137303 | GEO | 2019/09/13

REPOSITORIES: GEO

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Project description:The tomato psyllid, Bactericera cockerelli Šulc (Hemiptera: Triozidae), is a pest of solanaceous crops such as tomato (Solanum lycopersicum L.) in the U.S. and vectors the disease-causing pathogen ‘Candidatus Liberibacter solanacearum’ (or Lso). Lso disease symptom severity is dependent on Lso haplotype: tomato plants infected with Lso haplotype B experience more severe symptoms and higher mortality compared to plants infected with Lso haplotype A. By characterizing the molecular differences in the tomato plant’s responses to Lso haplotypes, the key components of LsoB virulence can be identified and, thus, targeted for disease mitigation strategies. To characterize the tomato plant genes putatively involved in the differential immune responses to Lso haplotypes A and B, RNA was extracted from tomato ‘Moneymaker’ leaves three weeks after psyllid infestation. Gene expression levels were compared between uninfected tomato plants (i.e., controls and plants infested with Lso-free psyllids) and infected plants (i.e., plants infested with psyllids infected with either Lso haplotype A or Lso haplotype B). Furthermore, expression levels were compared between plants infected with Lso haplotype A and plants infected with Lso haplotype B. A whole transcriptome analysis identified 578 differentially expressed genes (DEGs) between uninfected and infected plants as well as 451 DEGs between LsoA- and LsoB-infected plants. These DEGs were primarily associated with plant defense against abiotic and biotic stressors, growth/development, plant primary metabolism, transport and signaling, and transcription/translation. These gene expression changes suggested that tomato plants traded off plant growth and homeostasis for improved defense against pathogens, especially when infected with LsoB. Consistent with these results, tomato plant growth experiments determined that LsoB-infected plants were significantly stunted and had impaired negative geotropism. However, it appeared that the defense responses mounted by tomatoes were insufficient for overcoming the disease symptoms and mortality caused by LsoB infection, while these defenses could compensate for LsoA infection. The transcriptomic analysis and growth experiments demonstrated that Lso-infected tomato plants underwent gene expression changes related to abiotic and biotic stressors, impaired growth/development, impaired plant primary metabolism, impaired transport and signaling transduction, and impaired transcription/translation. Furthermore, the transcriptomic analysis also showed that LsoB-infected plants, relative to LsoA-infected, experienced more severe stunting, had improved responses to some stressors and impaired responses to others, had poorer transport and signaling transduction, and had impaired carbohydrate synthesis and photosynthesis.

Project description:Tomato seeds (S. lycopersicum ‘Fl Lanai’) were germinated under greenhouse conditions maintained at 24°C-29°C in flat trays (BWI Apopka, Catalog Number GPPF72S7X) filled with Sungro Horticulture soil (Metro-mix 830, BWI Apopka, Cat# TX830). Two weeks post emergence seedlings were transplanted to 4” pots using the same soil and transferred to a Conviron walk-in growth chamber (CMP6060) for the remainder of the experiment. Conviron conditions include a 14h/10h light/dark cycle maintained at 28°C, and plants were fertilized weekly (20-20-20). To prevent cross contamination, tomato plants were confined to insect proof cages at all times (BioQuip 1450NS68). Four weeks after transplanting, 40 whiteflies (B. tabaci MEAM1) were collected from virus free or Tomato Mottle Virus (ToMoV) established colonies via aspiration and moved into a clip cage placed on the 4th true leaf of each tomato plant as previously described38. Whiteflies were reared cabbage (Brassica oleracea), while viruliferous whiteflies were reared on ToMoV infected tomato from colonies established in the Polston lab. For all plants in this study, feeding was halted after 3 days of whitefly feeding (3 DPI) by gentle removal of clip cages and whitefly termination using insecticidal soap (Garden Safe, 1% of potassium salts of fatty acids). For the samples referred to as “local”, the tomato leaf bound within the clip cages was immediately removed and snap frozen for protein extraction. For the samples designated “systemic”, the plants were allowed to continue growing for 7 additional days after clip cage removal and whitefly termination, at which point the 9th leaf was excised and snap frozen. Plants used for collection of local leaves at 3 DPI were not used for the collection of systemic leaves 10 DPI. For both local and systemic leaves collected, we also included a no treatment control (NTC) that was subjected identically to clip cage and insecticidal soap applications, but without the addition of whitefly or ToMoV. Our experiment therefore consists of a no-treatment control (NTC), a whitefly treatment (+WF), and a viruliferous whitefly (+WFV) treatment for both local (4th true leaf, 3 DPI) and systemic leaves (9th true leaf, 10 DPI). The presence of ToMoV in all infected plants was confirmed via Nanopore sequencing. Briefly, Tomato genomic DNA was extracted from five systemic leaf samples using the PureGene tissue DNA isolation kit (product # 158667; QIAGEN, Valencia, CA, USA), following the manufacturer’s protocol and stored at -80°C until needed. Library preparation was performed using the Rapid Sequencing Kit RBK004 protocol (Oxford Nanopore Technologies) and loaded onto a 9.4.1 flow cell in a MinION connected to a MinIT with live base calling enabled. Resulting sequencing reads for each sample were mapped to both ToMoV A component (GenBank accession: L14460) and ToMoV B component (GenBank accession: L14461) sequences.

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Effect on tomato plants of asymptomatic infection with southern tomato virus

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