Abstract:
BACKGROUND: 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). 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.
RESULTS: 2.0 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.
CONCLUSIONS: This 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.
