Estudo dos mecanismos envolvidos na adaptabilidade diferencial de dois begomovírus em tomateiro e Nicotiana benthamiana / Study of the mechanisms involved in the diferential adaptability of two begomoviruses to tomato and Nicotiana benthamiana

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Begomoviruses belong to the family Geminiviridae, which includes viruses with a circular, single-stranded DNA genome encapsidated in twinned icosahedral particles. Begomoviruses are transmitted by the whitefly Bemisia tabaci, and cause serious diseases in several economically important crops, mostly in tropical and subtropical regions. In Brazil, a viral complex comprising at least eight species, including Tomato rugose mosaic virus (ToRMV) and Tomato yellow spot virus (ToYSV), is responsible for great losses in tomato production. ToYSV symptoms in tomato and Nicotiana benthamiana are more severe and appear earlier compared to ToRMV, suggesting differential adaptation of each virus to their hosts. We performed a series of experiments in order to analyze the role of a number of factors in this differential adaptation. The kinetics of viral infection was analyzed in plants which had the inoculated leaf removed at various periods of time after inoculation. Viral DNA accumulation was estimated in plants at 14 and 28 days post-inoculation (dpi). Viral replication was analyzed in protoplasts at 48 and 96 hours post- electroporation (hpe). Viral tissue tropism was analyzed by in situ hybridization at 14 dpi. Results indicate that ToYSV is more efficient in carrying out the early (pre-systemic) events of infection, reaching a higher concentration and establishing a systemic infection sooner and more efficiently than ToRMV in both tomato and N. benthamiana. In mixed infections, ToRMV negatively interferes on ToYSV during these initial stages of infection, but once a systemic infection is established this negative interference ceases. Both viruses are phloem-restricted in tomato. In N. benthamiana, ToYSV invades the mesophyll, while ToRMV is phloem-restricted. During mixed infection in this host, ToYSV releases ToRMV from the phloem. We conclude that ToYSV is better adapted than ToRMV to both hosts. In tomato, this is expressed by its reaching a higher concentration in a shorter period of time, which may lead to a higher accumulation of viral virulence factors. In N. benthamiana, it is further expressed by its ability to invade mesophyll cells.

ASSUNTO(S)

host-pathogen interaction geminivirus interação patógeno-hospedeiro fitopatologia geminivirus

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