Analysis of expressed sequence tags from Citrus sinensis L. Osbeck infected with Xylella fastidiosa

Alessandra A De Souza,Eduardo F Carlos,Helvécio D Coletta-Filho,Alexandre M Amaral,Raquel L Boscariol-Camargo,Ana Carla O Silva-Pinhati,Eliane C Locali-Fabris,Marco A Takita,Irving J Berger,Carolina M Rodrigues,Marcos A Machado,Juliana Freitas-Astúa,Maria Luisa P.N Targon,Marcelo S Reis

doi:10.1590/s1415-47572007000500023

Alessandra A De Souza, Eduardo F Carlos + Show 12 more

Open Access

https://doi.org/10.1590/s1415-47572007000500023

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Abstract

In order to understand the genetic responses resulting from physiological changes that occur in plants displaying citrus variegated chlorosis (CVC) symptoms, we adopted a strategy of comparing two EST libraries from sweet orange [Citrus sinensis (L.) Osbeck]. One of them was prepared with plants showing typical CVC symptoms caused by Xylella fastidiosa and the other with non-inoculated plants. We obtained 15,944 ESTs by sequencing the two cDNA libraries. Using an in silico hybridization strategy, 37 genes were found to have significant variation at the transcriptional level. Within this subset, 21 were up-regulated and 16 were down-regulated in plants with CVC. The main functional categories of the down-regulated transcripts in plants with CVC were associated with metabolism, protein modification, energy and transport facilitation. The majority of the up-regulated transcripts were associated with metabolism and defense response. Some transcripts associated with adaptation to stress conditions were up-regulated in plants with CVC and could explain why plants remain alive even under severe water and nutritional stress. Others of the up-regulated transcripts are related to defense response suggesting that sweet orange plants activate their defense machinery. The genes associated with stress response might be expressed as part of a secondary response related to physiological alterations caused by the infection.

Highlights

The citrus industry is one of most important agribusinesses in Brazil, with highly organized segments and competitive initiatives
The libraries were prepared from mRNA isolated from leaves of Pera sweet orange [C. sinensis (L.) Osbeck] grafted on Rangpur lime (C. limonia Osbeck) 24 months after grafting and growing under greenhouse conditions
From 6 to 8 months after inoculation, some infected plants showed citrus variegated chlorosis (CVC) symptoms and the presence of bacteria was confirmed by PCR using X. fastidiosa specific primers (Pooler and Hartung, 1995)

Summary

Introduction

The citrus industry is one of most important agribusinesses in Brazil, with highly organized segments and competitive initiatives. The symptoms occur as a result of the X. fastidiosa’s ability to colonize the xylem vessels and disrupt the transport of water and nutrients from the root system to the canopy (Hopkins, 1995) It affects all sweet orange varieties and can be transmitted by leafhoppers, contaminated budwood, and seedlings (Rossetti et al, 1990). The induction of abscisic acid (ABA), commonly observed in plants with water stress as a sinalization to stress response, was not observed in plants with CVC (Gomes et al, 2003), and plants colonized by X. fastidiosa had lower photosynthetic rates (Ribeiro et al, 2003) These changes occur in plants before symptoms develop and are probably caused by low stomatal conductance, biochemical injuries to the photosynthetic machinery, and increase in alternative electron sinks (Ribeiro et al, 2003). Comparative genomics was carried out through tentative consensus comparison against the GenBank protein database, using the Blastall implementation of BLAST algorithm (Altschul et al, 1997)

Materials and Methods

99. Unknown

63. Protein with binding function

Concluding Remarks