Abstract
BackgroundAvocado (Persea americana) belongs to the Lauraceae family and is an important commercial fruit crop in over 50 countries. The most serious pathogen affecting avocado production is Phytophthora cinnamomi which causes Phytophthora root rot (PRR). Root pathogens such as P. cinnamomi and their interactions with hosts are poorly understood and despite the importance of both the avocado crop and the effect Phytophthora has on its cultivation, there is a lack of molecular knowledge underpinning our understanding of defence strategies against the pathogen. In order to initiate a better understanding of host-specific defence we have generated EST data using 454 pyrosequencing and profiled nine defence-related genes from Pc-infected avocado roots.Results2.0 Mb of data was generated consisting of ~10,000 reads on a single lane of the GS FLX platform. Using the Newbler assembler 371 contigs were assembled, of which 367 are novel for Persea americana. Genes were classified according to Gene Ontology terms. In addition to identifying root-specific ESTs we were also able to identify and quantify the expression of nine defence-related genes that were differentially regulated in response to P. cinnamomi. Genes such as metallothionein, thaumatin and the pathogenesis related PsemI, mlo and profilin were found to be differentially regulated.ConclusionsThis is the first study in elucidating the avocado root transcriptome as well as identifying defence responses of avocado roots to the root pathogen P. cinnamomi. Our data is currently the only EST data that has been generated for avocado rootstocks, and the ESTs identified in this study have already been useful in identifying defence-related genes as well as providing gene information for other studies looking at processes such as ROS regulation as well as hypoxia in avocado roots. Our EST data will aid in the elucidation of the avocado transcriptome and identification of markers for improved rootstock breeding and screening. The characterization of the avocado transcriptome will furthermore form a basis for functional genomics of basal angiosperms.
Highlights
Avocado (Persea americana) belongs to the Lauraceae family and is an important commercial fruit crop in over 50 countries
expressed sequence tags (ESTs) identification and classifications After analysis using the dCAS software, 367 novel ESTs were identified for P. americana
The top ten functional groupings according to the GO classification revealed that 44.5% of assembled contigs were represented by unknown functions followed by the functional groups of ‘other’, ‘cellular components’, ‘biological processes’, ‘stress responses’, ‘ribosome structure’, ‘cell wall related’, ‘protein binding’, ‘mitochondrion and ‘ATP-binding’
Summary
Avocado (Persea americana) belongs to the Lauraceae family and is an important commercial fruit crop in over 50 countries. The most serious pathogen affecting avocado production is Phytophthora cinnamomi which causes Phytophthora root rot (PRR). Avocado (Persea americana Mill.) is an important agricultural crop in over 50 countries worldwide and is native to Mexico and Central America [1] It belongs to the genus-Persea, subgenus-Persea, family-Lauraceae and falls under the clade of magnoliids that are sister to eudicot and monodicot clades. Phytophthora root rot (PRR), caused by Phytophthora cinnamomi Rands, is considered the most destructive pathogen-induced disease to the avocado industry [2,3,4] with production relying heavily on the use of phosphite trunk injections and tolerant rootstocks such as Dusa® [4,5] supported by planting in high organic matter soils and mulching to promote antagonistic microbial growth against P. cinnamomi. This decreased sensitivity to phosphite could indicate the onset of resistance to the fungicide
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