Medicago truncatula as a Model for Nonhost Resistance in Legume-Parasitic Plant Interactions

Abstract

Crenate broomrape (Orobanche crenata) is a root parasitic weed that represents a major constraint for grain legume production in Mediterranean and West Asian countries. Medicago truncatula has emerged as an important model plant species for structural and functional genomics. The close phylogenic relationship of M. truncatula with crop legumes increases its value as a resource for understanding resistance against Orobanche spp. Different cytological methods were used to study the mechanisms of resistance against crenate broomrape of two accessions of M. truncatula, showing early and late acting resistance. In the early resistance accession (SA27774) we found that the parasite died before a tubercle had formed. In the late resistance accession (SA4327) the parasite became attached without apparent problems to the host roots but most of the established tubercles turned dark and died before emergence. The results suggest that there are defensive mechanisms acting in both accessions but with a time gap that is crucial for a higher success avoiding parasite infection.Crenate broomrape (Orobanche crenata) is one of the most important parasitic plants attacking legume crops in Mediterranean area, devastating crops and making unusable infested land (Rubiales, 2001(Rubiales, , 2003Rubiales et al., 2002). Being a broomrape (Orobanche sp.), crenate broomrape is an obligate root holoparasite lacking in chlorophyll and depending entirely on the host for its supply of nutrients (Joel et al., 2007). The knowledge of the mechanisms of resistance against the parasite is crucial to develop strategies of control, like breeding for resistance. With this purpose, we have chosen Medicago truncatula as a crenate broomrape host model plant due to its characteristics.M. truncatula is an annual forage legume in the Mediterranean area. Contrary to other legume crops, M. truncatula is an autogamous self-fertile plant with a small and diploid genome, a short life cycle, and a prolific seed production (Blondon et al., 1994). Its simple genetics, the development of new tools and methods for molecular and genetic analysis, and the complete genome sequence (http://www.medicago.org) provide researchers with a valuable data set and making it interesting as a legume model species for laboratory studies (Cook et al., 1997;Cook, 1999) and also in pathogenic interactions (Ellwood et al., 2007; Pérez-de-Luque et al., 2007a).Nowadays, the most numerous and important works about parasitic plants were focused on the development in susceptible host, as Orobanche spp. (Joel and Losner-Goshen, 1994;Neumann et al., 1999), Striga spp. (Dörr, 1997;Reiss and Bailey, 1998), Cuscuta spp. (Vaughn, 2002(Vaughn, , 2003, Viscum spp. (Heide-Jørgensen, 1987), and others (Heide-Jørgensen and Kuijt, 1993, 1995). But little is known about the basis of host resistance to these parasites, just finding the work of Joel et al. (1996) introducing this subject. In the last years only some histological studies of the resistant interactions have been undertaken (Dörr et al., 199...

Perfil da alteração na produção de substâncias fenólicas e açúcares livres na interação entre Tapirira guianensis Aubl. (Anacardiaceae) parasitada por Phoradendron crassifolium (Pohl ex DC.) Eichler (Santalaceae)

“…Deste modo pesquisas sobre os mecanismos de defesa que atuam nessa relação de parasitismo têm sido realizadas com o objetivo de desenvolver estratégias de controle, principalmente para parasitas de espécies agronomicamente importantes (Lozano-Baena et al, 2007).…”

“…Essa escassez de informação pode ser justificada devido à complexidade existente nessa relação de parasitismo, visto que ela envolve organismos pertencentes ao mesmo grupo, isto é, duas plantas, acarretando em um compartilhamento de aspectos bioquímicos, fisiológicos e morfológicos (Lozano-Baena et al, 2007).…”

“…Vale ressaltar que a defesa de plantas contra plantas parasitas, assim como a qualquer outro fator de estresse, não envolve apenas uma resposta, mas sim uma combinação de alterações que comporão o mecanismo de defesa (Lozano-Baena et al, 2007).…”

“…Outras respostas de defesa já relatadas para a relação de parasitismo entre plantas são a redução na produção de estimulantes de germinação (Jamil et al, 2011), deposição de calose, suberização (Echevarría-Zomeño et al, 2006) e produção de metabólitos secundários, especialmente substâncias fenólicas (Hariri et al, 1991;Goldwasser et al, 1999;Echevarría-Zomeño et al, 2006;Lozano-Baena et al, 2007).…”

“…Segundo Hariri et al (1991), flavonoides constituiriam um mecanismo de defesa por contribuírem para a rejeição do patógeno em duas formas: agindo como substâncias tóxicas (como ocorre em alguns casos de associações fungo-planta) ou agindo como barreira química para a parasita. Alguns autores sugerem que a liberação de substâncias fenólicas pela planta hospedeira tornaria o ambiente celular quimicamente hostil para as células intrusivas da planta parasita (Echevarría-Zomeño et al, 2006;Lozano-Baena et al, 2007).…”