Understanding the changes affecting the plant cell wall is a key element in addressing its functional role in plant growth and in the response to stress. Pectins, which are the main constituents of the primary cell wall in dicot species, play a central role in the control of cellular adhesion and thereby of the rheological properties of the wall. This is likely to be a major determinant of plant growth. How the discrete changes in pectin structure are mediated is thus a key issue in our understanding of plant development and plant responses to changes in the environment. In particular, understanding the remodelling of homogalacturonan (HG), the most abundant pectic polymer, by specific enzymes is a current challenge in addressing its fundamental role. HG, a polymer that can be methylesterified or acetylated, can be modified by HGMEs (HG-modifying enzymes) which all belong to large multigenic families in all species sequenced to date. In particular, both the degrees of substitution (methylesterification and/or acetylation) and polymerization can be controlled by specific enzymes such as pectin methylesterases (PMEs), pectin acetylesterases (PAEs), polygalacturonases (PGs), or pectate lyases-like (PLLs). Major advances in the biochemical and functional characterization of these enzymes have been made over the last 10 years. This review aims to provide a comprehensive, up to date summary of the recent data concerning the structure, regulation, and function of these fascinating enzymes in plant development and in response to biotic stresses.

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Homogalacturonan-modifying enzymes: structure, expression, and roles in plants

The tomato is an excellent model for studies of plants bearing berry-type fruits and for experimental studies of the Solanaceae family of plants due to its conserved genetic organization. In this study, a comprehensive mutant tomato population was generated in the background of Micro-Tom, a dwarf, rapid-growth variety. In this and previous studies, a family including 8,598 and 6,422 M2 mutagenized lines was produced by ethylmethane sulfonate (EMS) mutagenesis and γ-ray irradiation, and this study developed and investigated these M2 plants for alteration of visible phenotypes. A total of 9,183 independent M2 families comprising 91,830 M2 plants were inspected for phenotypic alteration, and 1,048 individual mutants were isolated. Subsequently, the observed mutant phenotypes were classified into 15 major categories and 48 subcategories. Overall, 1,819 phenotypic categories were found in 1,048 mutants. Of these mutants, 549 were pleiotropic, whereas 499 were non-pleiotropic. Multiple different mutant alleles per locus were found in the mutant libraries, suggesting that the mutagenized populations were nearly saturated. Additionally, genetic analysis of backcrosses indicated the successful inheritance of the mutations in BC1F2 populations, confirming the reproducibility in the morphological phenotyping of the M2 plants. To integrate and manage the visible phenotypes of mutants and other associated data, we developed the in silico database TOMATOMA, a relational system interfacing modules between mutant line names and phenotypic categories. TOMATOMA is a freely accessible database, and these mutant recourses are available through the TOMATOMA (http://tomatoma.nbrp.jp/index.jsp).

http://www.genopomii.unina.it/genohort/files/2_TOMATOMA%20A%20Novel%20Tomato%20Mutant%20Database.pdf

TOMATOMA : A Novel Tomato Mutant Database Distributing Micro-Tom Mutant Collections

To accelerate functional genomic research in tomato, we developed a Micro-Tom TILLING (Targeting Induced Local Lesions In Genomes) platform. DNA pools were constructed from 3,052 ethyl methanesulfonate (EMS) mutant lines treated with 0.5 or 1.0% EMS. The mutation frequency was calculated by screening 10 genes. The 0.5% EMS population had a mild mutation frequency of one mutation per 1,710kb, whereas the 1.0% EMS population had a frequency of one mutation per 737kb, a frequency suitable for producing an allelic series of mutations in the target genes. The overall mutation frequency was one mutation per 1,237kb, which affected an average of three alleles per kilobase screened. To assess whether a Micro-Tom TILLING platform could be used for efficient mutant isolation, six ethylene receptor genes in tomato (SlETR1–SlETR6) were screened. Two allelic mutants of SlETR1 (Sletr1-1 and Sletr1-2) that resulted in reduced ethylene responses were identified, indicating that our Micro-Tom TILLING platform provides a powerful tool for the rapid detection of mutations in an EMS mutant library. This work provides a practical and publicly accessible tool for the study of fruit biology and for obtaining novel genetic material that can be used to improve important agronomic traits in tomato.

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Tomato TILLING Technology: Development of a Reverse Genetics Tool for the Efficient Isolation of Mutants from Micro-Tom Mutant Libraries

The protective Fusarium oxysporum strain Fo47 is effective in controlling Fusarium wilt in tomato. Previous studies have demonstrated the role of direct antagonism and involvement of induced resistance. The aim of the present study was to investigate whether priming of plant defense responses is a mechanism by which Fo47 controls Fusarium wilt. An in vitro design enabled inoculation of the tap root with Fo47 and the pathogenic strain (Fol8) at different locations and different times. The expression levels of six genes known to be involved in tomato defense responses were quantified using reverse-transcription quantitative polymerase chain reaction (qPCR). Three genes-CHI3, GLUA, and PR-1a-were overexpressed in the root preinoculated with Fo47, and then challenged with Fol8. The genes GLUA and PR-1a were upregulated in cotyledons after inoculation of Fo47. Fungal growth in the root was assessed by qPCR, using specific markers for Fo47 and Fol8. Results showed a reduction of the pathogen growth in the root of the tomato plant preinoculated with Fo47. This study demonstrated that priming of tomato defense responses is one of the mechanisms of action of Fo47, which induces a reduced colonization of the root by the pathogen.

https://apsjournals.apsnet.org/doi/pdf/10.1094/MPMI-12-12-0290-R

The endophytic strain Fusarium oxysporum Fo47: a good candidate for priming the defense responses in tomato roots.

Summary

The expression pattern of pathogenesis-related genes PR-1, PR-2 and PR-5, considered as markers for salicylic acid (SA)-dependent systemic acquired resistance (SAR), was examined in the roots and shoots of tomato plants pre-treated with SA and subsequently infected with root-knot nematodes (RKNs) (Meloidogyne incognita). PR-1 was up-regulated in both roots and shoots of SA-treated plants, whereas the expression of PR-5 was enhanced only in roots. The over-expression of PR-1 in the whole plant occurred as soon as 1 day after SA treatment. Up-regulation of the PR-1 gene was considered to be the main marker of SAR elicitation. One day after treatment, plants were inoculated with active juveniles (J2s) of M. incognita. The number of J2s that entered the roots and started to develop was significantly lower in SA-treated than in untreated plants at 5 and 15 days after inoculation. The expression pattern of PR-1, PR-2 and PR-5 was also examined in the roots and shoots of susceptible and Mi-1-carrying resistant tomato plants infected by RKNs. Nematode infection produced a down-regulation of PR genes in both roots and shoots of SA-treated and untreated plants, and in roots of Mi-carrying resistant plants. Moreover, in resistant infected plants, PR gene expression, in particular PR-1 gene expression, was highly induced in shoots. Thus, nematode infection was demonstrated to elicit SAR in shoots of resistant plants. The data presented in this study show that the repression of host defence SA signalling is associated with the successful development of RKNs, and that SA exogenously added as a soil drench is able to trigger a SAR-like response to RKNs in tomato.

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Expression of tomato salicylic acid (SA)-responsive pathogenesis-related genes in Mi-1-mediated and SA-induced resistance to root-knot nematodes.

To understand the machinery underlying a tomato cultivar harboring the Hero A gene against cyst nematode using microarrays, we fi rst analyzed tomato gene expression in response to potato cyst nematode (PCN; Globodera rostochiensis ) during the early incompatible and compatible interactions at 3 and 7 days post-inoculation (dpi). Transcript levels of the phenylalanine ammonia lyase ( PAL ) and Myb related genes were up-regulated at 3 dpi in the incompatible interaction. Transcription of the genes encoding pyruvate decarboxylase ( PDC ) and alcohol dehydrogenase ( ADH ) was also up-regulated at 3 dpi in the incompatible interaction. On the other hand, the four genes ( PAL , Myb , PDC and ADH ) were down-regulated in the compatible interaction at 3 dpi. When the expression levels of several pathogenesis-related (PR) protein genes in tomato roots were compared between the incompatible and compatible interactions, the salicylic acid (SA)-dependent PR genes were found to be induced in the incompatible interaction at 3 dpi. The PR-1 ( P4 ) transcript increased to an exceptionally high level at 3 dpi in the cyst nematode-infected resistant plants compared with the uninoculated controls. The free SA levels were elevated to similar levels in both incompatible and compatible interactions. We then confi rmed that PR-1 ( P4 ) was not signifi cantly induced in the NahG tomato harboring the Hero A gene, compared with the resistant cultivar. We thus found that PR-1 ( P4 ) was a hallmark for the cultivar resistance conferred by Hero A against PCN and that nematode parasitism resulted in the inhibition of the SA signaling pathway in the susceptible cultivars.

/pdf/resistant-and-susceptible-responses-in-tomato-to-cyst-92xzc75fvq.pdf

Resistant and susceptible responses in tomato to cyst nematode are differentially regulated by salicylic acid.

We analyzed global transcripts for tomato roots infected with the cyst nematode Globodera rostochiensis using serial analysis of gene expression (SAGE). SAGE libraries were made from nematode-infected roots and uninfected roots at 14 days after inoculation, and the clones including SAGE tags were sequenced. Genes were identified by matching the SAGE tags to tomato expressed sequence tags and cDNA databases. We then compiled a list of numerous genes according to the mRNA levels that were altered after cyst nematode infection. Our SAGE results showed significant changes in expression of many unreported genes involved in nematode infection. Of these, for discussion we selected five SAGE tags of RSI-1, BURP domain-containing protein, hexose transporter, P-rich protein, and PHAP2A that were activated by cyst nematode infection. Over 20% of the tags that were upregulated in the infected root have unknown functions (non-annotated), suggesting that we can obtain information on previously unreported and uncharacterized genes by SAGE. We can also obtain information on previously reported genes involved in nematode infection (e.g., multicystatin, peroxidase, catalase, pectin esterase, and S-adenosylmethionine transferase). To evaluate the validity of our SAGE results, seven genes were further analyzed by semiquantitative reverse transcriptase–polymerase chain reaction and Northern blot hybridization; the results agreed well with the SAGE data.

Comparative serial analysis of gene expression of transcript profiles of tomato roots infected with cyst nematode

A simple, sensitive, specific detection of mixed infection of multiple plant viruses using macroarray and microtube hybridization

The potato cyst nematode (PCN) Globodera rostochiensis (Wollenweber) was first found in Japan in 1972 in a potato field of Makkari Village in Hokkaido (Yamada et al., 1972). PCN subsequently spread to other parts of Hokkaido and has become a serious problem in many potato-growing areas, causing substantial yield reductions. All eggs of PCN are produced inside the female body, which becomes a cyst with a hardened protective wall upon death. This structure protects the eggs from rapid desiccation and enhances their ability to remain viable for many years. In a potato field, the main scheme for integrated control is based on crop rotation with non-host crops and potato cultivars resistant to the nematode (Inagaki, 1984; Yamada, 1987; Whitehead and Turner, 1998). PCN can also multiply on tomato plants and has been reported as a problem plaguing tomatoes in Europe (Graham, 1966; Ellis, 1968; Ellis and Maxon Smith, 1971; Hesling and Ellis, 1972; Trifonova et al., 1995). Some susceptible tomato cultivars were severely stunted by infection with high initial numbers of nematodes (Hesling and Ellis, 1972). In Hokkaido, where areas of tomato cultivation have increased, the susceptible cultivar Momotaro-8 was also found to be stunted by PCN. Therefore, PCN is now regarded as a new tomato pest in Hokkaido (Hokkaido Plant Protection Office, 1997), and it has become necessary to find PCN-resistant cultivars and resistant rootstocks. Recently, we found several tomato cultivars and one tomato rootstock cultivar that show strong resistance to PCN (Uehara et al., 2008). The usefulness of cyst nematode-resistant potato cultivars for controlling the nematode has been recognized in several studies (Inagaki, 1978; Trudgill et al., 1978; Yamada and Takakura, 1981; Whitehead, 1991), whereas the usefulness of cyst nematode-resistant tomato cultivars has not been studied in detail. In the present study, we investigated the effectiveness of cyst nematode-resistant tomato cultivars in reducing the population of PCN in greenhouse trials.

Decrease in Globodera rostochiensis (Wollenweber) (Nematode: Heteroderidae) population density on resistant tomato cultivars in greenhouse trials

Potato cyst nematodes (PCNs) Globodera rostochiensis (Woll.) and G. pallida Stone are major pests of potato growing areas worldwide (Brodie et al., 1998). PCNs are classified into pathotypes on the basis of their ability to multiply on different potato clones. Kort et al. (1977) proposed the International Scheme for Globodera pathotypes in which, among the European populations, five pathotypes within G. rostochiensis and three pathotypes within G. pallida were recognized. In Japan, G. rostochiensis was first found in 1972 within a potato field in Makkari Village, Hokkaido (Yamada et al., 1972). It subsequently spread to other parts of Hokkaido and other districts in Japan. Globodera rostochiensis pathotype Ro1 is the only species and pathotype present in Japan (Kushida and Momota 2005). PCN can also reproduce on tomato and has been reported as a problem for tomato growing regions in Europe (Ellis, 1968; Ellis and Maxon Smith, 1971; Graham, 1966; Hesling and Ellis, 1972; Trifonova et al., 1995). In Hokkaido, it was also reported that PCN was detected in tomato plants (Hokkaido Plant Protection Office, 1997). In good agricultural practice, nematodes are controlled by crop rotation and the use of nematocides and resistant cultivars. The exploitation of host resistance is the most effective and environmentally benign method for managing plant nematodes. Several PCN resistance genes have been characterized genetically within Solanum species and have been exploited successfully in potato breeding (Ross, 1986). For example, the dominant nematode resistance gene H1 from S. tuberosum ssp. andigena (Ellenby, 1954) has been used extensively to provide a high level of durable resistance against G. rostochiensis pathotypes Ro1 and Ro4 within potato cultivars worldwide (Brodie et al., 1998; Ross, 1986). Recently, we found a number of Japanese tomato cultivars with resistance to G. rostochiensis (Uehara et al., 2008). A PCN resistance gene, Hero, was identified in a wild tomato variety, and this gene was introgressed into the tomato breeding line LA1792 (Ellis and MaxonSmith, 1971). Cabrera Poch et al. (2006) reported that the HERO_F2/HERO_R3 primer pair could be used to amplify two closely sized DNA fragments from tomato breeding line LA1792 (resistant) and one fragment from the cultivar Moneymaker (susceptible). Using the HERO_F2/HERO_R3 primer pair, we also confirmed that the tested resistant tomato cultivars in Japan contained the Hero A gene, whereas susceptible cultivars did not (Uehara et al., 2010). When this primer pair was used, however, the two DNA fragments from resistant cultivars were located very close to each other after electrophoresis. Therefore, we tried to develop a distinct DNA marker for Hero A. We then used these new distinct polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) markers to evaluate our Detection of the potato cyst nematode resistance gene Hero A in Japanese tomato cultivars by the PCR-RFLP method

Taketo Uehara

Papers

Resistant and susceptible responses in tomato to cyst nematode are differentially regulated by salicylic acid.

Comparative serial analysis of gene expression of transcript profiles of tomato roots infected with cyst nematode

A simple, sensitive, specific detection of mixed infection of multiple plant viruses using macroarray and microtube hybridization

Decrease in Globodera rostochiensis (Wollenweber) (Nematode: Heteroderidae) population density on resistant tomato cultivars in greenhouse trials

Detection of the potato cyst nematode resistance gene Hero A in Japanese tomato cultivars by the PCR-RFLP method