Abstract
The NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 (NPR1) forms an integral part of the salicylic acid (SA) pathway in plants and is involved in cross-talk between the SA and jasmonic acid/ethylene (JA/ET) pathways. Therefore, NPR1 is essential to the effective response of plants to pathogens. Avocado (Persea americana) is a commercially important crop worldwide. Significant losses in production result from Phytophthora root rot, caused by the hemibiotroph, Phytophthora cinnamomi. This oomycete infects the feeder roots of avocado trees leading to an overall decline in health and eventual death. The interaction between avocado and P. cinnamomi is poorly understood and as such limited control strategies exist. Thus uncovering the role of NPR1 in avocado could provide novel insights into the avocado – P. cinnamomi interaction. A total of five NPR1-like sequences were identified. These sequences were annotated using FGENESH and a maximum-likelihood tree was constructed using 34 NPR1-like protein sequences from other plant species. The conserved protein domains and functional motifs of these sequences were predicted. Reverse transcription quantitative PCR was used to analyze the expression of the five NPR1-like sequences in the roots of avocado after treatment with salicylic and jasmonic acid, P. cinnamomi infection, across different tissues and in P. cinnamomi infected tolerant and susceptible rootstocks. Of the five NPR1-like sequences three have strong support for a defensive role while two are most likely involved in development. Significant differences in the expression profiles of these five NPR1-like genes were observed, assisting in functional classification. Understanding the interaction of avocado and P. cinnamomi is essential to developing new control strategies. This work enables further classification of these genes by means of functional annotation and is a crucial step in understanding the role of NPR1 during P. cinnamomi infection.
Highlights
Plants recognize and react to external threats much like any other living organism, eliciting a response to combat disease (Robert-Seilaniantz et al, 2011)
We identified five NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 (NPR1)-like genes in avocado in an attempt to better understand avocado defense response signaling in general, and with regard to the response to Phytophthora root rot (PRR)
This study is the first investigation of the NPR1-like gene family in P. americana, and sets the foundation for further functional characterization of the NPR1-like protein family in avocado
Summary
Plants recognize and react to external threats much like any other living organism, eliciting a response to combat disease (Robert-Seilaniantz et al, 2011). The most extensively studied member of the Arabidopsis NPR1-like family is AtNPR1 Mutants of this protein are more susceptible to virulent pathogens and display compromised expression of PR genes when compared to plants expressing wild-type NPR1 (Glazebrook et al, 1996; Cao et al, 1997). NPR1 interacts with several members of the TGACG motif-binding factor (TGA) family of basic leucine zipper protein (bZIP) transcriptions factors (Zhang et al, 1999; Despres et al, 2000; Zhou et al, 2000) These transcription factors associate with the as-1-like (TGACG) promoter element within PR gene promoters and are responsible, at least in part, for their expression (Fan and Dong, 2002; Zhang et al, 2003). Future efforts could focus on intracellular interactions and localization as well as overexpression of defense related PaNPR1-like genes in wild-type and npr mutant Arabidopsis
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