Identificação de genes diferencialmente expressos na interação tomateiro - Alternaria solani

• Autor(a) principal: Scheuermann, Klaus Konrad
• Data de Publicação: 2006
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1070
• topic: Tomate - Resistência à Alternaria solani; Pinta-preta; Relação planta-patógeno; Regulação de expressão gênica; Biologia molecular; Tomato - Alternaria solani resistance; Early blight; Plant-pathogen relationship; Regulation of gene expression; Molecular biology; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOSSANIDADE::FITOPATOLOGIA

The tomato early blight, caused by the fungus Alternaria solani Sor., is considered one of the most important diseases of this crop causing yield losses that can reach about 80%. The development of resistant cultivars has been difficult because the resistance is polygenic and germoplasm with adequate levels of resistance to the pathogen is not available. In order to identify genes involved with tomato defense responses against A. solani, two cDNA libraries were constructed from mRNA isolated from leaf samples of the lineage NC EBR2 collected at 24 and 36 hours after inoculation (hai) by using the suppressive subtractive hybridization (SSH) technique. Sequence analysis of 1303 ESTs revealed that 31% of them showed similarities with plant defense genes, regulation of gene expression and transduction signals. Among the putative genes related with defense mechanisms, there was predominance of genes regulated by ethylene and jasmonic acid and a lower frequency of ESTs with similarities to genes regulated by salicylic acid. Real time PCR analysis (RT-qPCR) of 40 genes showed that 16 of them (40%) were induced in response to fungus infection. The induction of the majority of these genes began between 6 and 12 hai, reaching a maximum between 24 and 36 hai. Considering that host resistance to early blight is associated with tissue age, the level of gene expression in older (1st and 2nd) and younger (4th and 5th) leaves were compared from 45 days old plants. Genes coding for PR-1 basic p1-p14, basic β-1,3-endoglucanase, NtEIG-A1 (Nicotiana tabacum protein A1), THT1-3 (N-hydroxycinnamoyl-CoA tyramine N-hydroxycinnamoyl transferase) , POTLX- 3 (Lipoxygenase-3) and pSTH-2 (PR STH2 protein) had a higher level of expression in younger leaves. Moreover, it was observed that genes like NtEIG- A1 had a faster response in younger leaves. High level of defense genes expression associated with a faster response can be one of the mechanisms responsible for the reduced level of disease severity in the younger tomato leaves.