Phylogenetic and expression analysis of the NPR1-like gene family from Persea americana (Mill.)

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.

Expresión diferencial de genes de defensa en aguacate en respuesta a la infección del viroide de la mancha de sol del aguacate

“…Sin embargo, los resultados siguieren que los cambios de expresión de PR-5 en tejidos infectados por ASBVd no fueron inducidos por PaNPR1, debido a que los niveles de expresión de éste no muestran diferencias significativas con respecto a la expresión basal. Backer et al (2015) reportaron que la expresión constitutiva basal de PaNPR1 fue más alta en hojas que en frutos inmaduros; además, y a diferencia del conocimiento que se tiene donde el ácido salicílico es activador de NPR1, los autores encontraron una regulación negativa de PaNPR1 en el tratamiento con ácido salicílico a las 12h después de la aplicación, lo que sugiere una función alternativa en las respuestas de defensa.…”

“…However, results in this research suggest that changes in PR-5 expression on tissue infected by ASBVd were not produced by changes in PaNPR1 expression because it did not change significantly from basal. Backer et al (2015) reported that PaNPR1 constitutive expression was higher on leaves than on unripe fruits. Additionally, and contrary to documented reports on NPR1 activation by salicylic acid, they found PaNPR1 down-regulation 12 h after salicylic acid treatment; this behavior suggests an alternative function for defense responses.…”

“…Four genes associated with pathogen defense in avocado were selected: PaNPR1 (Backer et al, 2015), PR-5, PR-6 and EREBP (Djami-Tchatchou et al, 2013). The actin gene (Reeksting et al, 2014) was used as a reference gene.…”

Evaluation of phytophthora root rot resistance in avocado

“…observed that resistance of avocado roots to P. cinnamomi infection was associated with more rapid β-1,3-glucanase and superoxide dismutase activities as soon as 6 hpi in a resistant variety. By measuring expression levels of five defence-related NPR1-like genes after treatment with salicylic acid (SA), jasmonic acid (JA) and inoculation with P. cinnamomi, Backer et al (2015) found that at 12 hpi, expression of PaNPR2 and PaNPR4 was significantly lower in the resistant variety 'Dusa' than in the susceptible variety 'R0.12'. It is suggested that the switch from biotrophic to necrotrophic growth may occur around this time, and that in 'R0.12', increased expression of PaNPR1-like defence-related genes may suppress the JA/ET pathway, relative to 'Dusa', which perceives and reacts to the change in growth habit more quickly.…”

“…These aspects of resistance include the following: (I) root regenerative ability , (II) attractiveness to zoospores in terms of either encystment rates (Aveling & Rijkenberg, 1991 or the concentration and composition of exudates produced by the roots , Zilberstein & Pinkas, 1987, (III) deposition of structural barriers such as callose and tyloses , Dugger & Zentmyer, 1981, (IV) the induction of various biochemical defence pathways within avocado roots in response to P. cinnamomi infection , García-Pineda et al, 2010, Romero-Correa et al, 2014, Backer et al, 2015. The approaches outlined above involve identification of a resistant phenotype before association with the corresponding genotype.…”