Abstract
Citrus Tristeza disease, caused by CTV (Citrus tristeza virus), committs citrus plantations around the world and specifically attacks phloem tissues of the plant. The virus exists as a mixture of more or less severe variants, which may or may not cause symptoms of Tristeza. The objective of this study was to analyze the changes caused by CTV in the proteome of stems of sweet orange, as well as in the activity and gene expression of antioxidant enzymes. The CTV-infected sweet orange displayed mild symptoms, which were characterized by the presence of sparse stem pitting throughout their stems. The presence of virus was confirmed by RT-PCR. Proteomic analysis by 2DE-PAGE-MS / MS revealed the identity of 40 proteins differentially expressed between CTV- infected and -non-infected samples. Of these, 33 were up-regulated and 7 were down-regulated in CTV-infected samples. Among the proteins identified stands out a specific from the virus, the coat protein. Other proteins identified are involved with oxidative stress and for this their enzymatic activity was measured. The activity of superoxide dismutase (SOD) was higher in CTV-infected samples, as catalase (CAT) showed higher activity in uninfected samples. The activity of guaiacol peroxidase (GPX) did not vary significantly between samples. However, ascorbate peroxidase (APX) was more active in the infected samples. The relative expression of the genes encoding CAT, SOD, APX and GPX was analyzed by quantitative real time PCR (RT-qPCR). The CTV-infected samples showed greater accumulation of transcripts, except for the CAT gene. This gene showed higher expression in the uninfected samples. Taken together, it can be concluded that the CTV affects the protein profile and activity and gene expression of antioxidant enzymes in plants infected by this virus.
Highlights
Among the fruits which are consumed raw and used industrially, citrus fruits represent the main world demand [1]
Branch bark proteins in Citrus tristeza virus (CTV)-infected and non-infected citrus plants of Westin variety were separated in 2D gels
It was demonstrated that sweet orange variety “Westin” responds to the presence of CTV with variations in its protein profile, and in the expression of specific genes
Summary
Among the fruits which are consumed raw and used industrially, citrus fruits represent the main world demand [1]. Around 60% of the orange juice consumed in the world comes from Brazilian orchards, which dominate the international market for that fruit [2]. The losses caused by diseases represent a major problem for citriculture. Tristeza is one of those diseases which affect citriculture throughout the world [3]. The disease is caused by Citrus tristeza virus (CTV), a member of genus Closterovirus which belongs to family Closteroviridae [4]. Resistant plants do not multiply the virus—if they do, it is a much reduced multiplication. Tolerant plants allow for that multiplication, but they tolerate the virus presence in their tissues, but do not develop symptoms of the disease [5]
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