Cinética dos fatores de iniciação da tradução em Vigna unguiculata L. (WALP.) e estratégias de tolerância de Nicotiana tabacum L. (VAR. XHANTI) frente à inoculação com o vírus do mosaico severo do CAUPI (CPSMV), um patógeno natural de plantas leguminosas

Abstract

The virus diseases are the major cause of crop yield loss. The Cowpea Severe Mosaic Virus (CPSMV), a virus from the genus Comovirus, specifically infects cowpea (Vigna unguiculata L.), an important crop worldwide. This study mainly aimed to indicate mechanisms for plant defense against CPSMV, specifically using resistant and susceptible genotypes of cowpea (Vigna unguiculata L. Walp.) and in vitro-cultivated tobacco seedlings (Nicotiana tabacum L. var. Xanthi) as study models. First, the transcriptional responses of the translation initiation factor 4E (eIF4E) and its isoform (eIF(iso)4E) in response to CPSMV infection were studied in leaves of five V. unguiculata genotypes with different levels of virus resistance. The results showed that the transcription of eIF4E and eIF(iso)4E were modulated after CPSMV infection depending on the degree of susceptibility of each genotype tested. In a second experiment, leaves of tobacco plantlets grown in vitro were CPSMV- and mock-inoculated and the results were evaluated at 1, 2 and 6 days post-inoculation. Although no visual symptoms were observed, CPSMV-capsid protein accumulation was detected in infected leaves, in addition to lower accumulation of soluble proteins and RNA. Additionally, a H2O2 accumulation was observed mainly between the first and the second day after the virus inoculation. CPSMV modulated the activities of some defense-related enzymes and transcript expression in tobacco to its own benefit, as revealed by down-regulation of genes involved in plant defense (RDR2, NR, BRI1, and BAK1), increase in glucanase activity, and up-regulation of the transcription initiation factor eIF4E, which is related to CPSMV protein synthesis, replication, and spread. On the other hand, tobacco plantlets attempted to overcome the viral infection by modulation of the H2O2 and phenolic compound contents, and the activities of related enzymes (superoxide dismutase, ascorbate peroxidase, phenylalanine ammonia-lyase, and guaiacol peroxidase), exhibiting patterns of a tolerant plant. Altogether it appears that N. tabacum is CPSMV-tolerant because it responds with higher H2O2 and phenolic compound production and increased activity of some defense-related enzymes.