Molecular, biochemical and microscopic aspects of the cassava-Xanthomonas anoxopodis pv. manihotis interaction

• Ano de defesa: 2014
• Autor(a) principal: Freitas, Cecília Chagas de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Mandioca - Doenças e pragas; Xanthomonas axonopodis pv. manihotis; qRT-PCR; Fitopatologia
• Link de acesso: https://locus.ufv.br//handle/123456789/27449

Cassava (Manihot esculenta), cultivated essentially in tropical and subtropical regions, is the fourth most important food crop in the world.. Cassava bacterial blight (CBB) caused Xanthomonas axonopodis pv. manihotis (Xam) is one of the most important cassava diseases, causing yield losses that can reach 100%. However, information about the molecular and biochemical mechanisms involved in Xam-cassava interaction as well as its vascular translocation inside cassava vessels is still limited. To get insight into the mechanisms involved in the defense response of the susceptible and resistant cassava cultivars, Cacau and Fécula Branca, respectively, against Xam, were analyzed the activities of the defense-related proteins peroxidase (POX), polyphenol oxidase (PPO), catalase (CAT), β,1-3- glucanase (GLU), chitinase (CHI), and phenylalanine ammonialyase (PAL), including the accumulation of hydrogen peroxide (H 2 O 2 ), and malondialdehyde (MDA). Using RT-qPCR, the expression profile of the defense-related genes peroxidase (POX 72), catalase (CAT2), β,1-3- glucanase (GLU), chitinase (CHI), pathogenesis related protein 5 osmotin (PR-5), ethylene ERF2 (ET) and CC-NBS-LRR like protein (CC) was studied. In addition, the vascular translocation of Xam was analyzed by confocal laser scanning microscopy using a GFP-tagged isolate. CCB incidence and Xam population was significantly lower on Fécula-branca when compared to Cacau. POX, PPO and GLU activities were detected 24 hours after inoculation (hai) in Fécula-branca. In contrast, activity on Cacau could be detected only about 72 hai. In addition, PAL, CHI, and CAT activity was higher in Fécula-branca. The MDA concentration did not show any correlation with the disease progress and the H 2 O 2 concentration presented a peak at 120 hai exactly at the decrease of bacterial growth. Based on RT-qPCR, POX, GLU, and PR-5 expression was detected earlier on the resistant cultivar (24 hai) in contrast to the susceptible one (72 hai for POX and GLU; 120 hai for PR-5). ET, CAT, and CHI expression was higher on Fécula Branca and CC expression did not show any response. Xam-GFP vascular translocation could be detected at 6 cm downstream and upstream on cassava stems. Altogether, these results show that a more efficient cassava defense response based on the activity and expression of defense-related proteins and genes, respectively, limited bacterial growth thus contributing to cassava resistance to CBB.