Fig 1.
Phytophthora cinnamomi (Pc) infection of resistant avocado roots.
A. Scanning electron micrograph of two Pc cysts germinating, with hyphae entering the root at the same site via direct penetration 1 hpi. B. Confocal image of Pc hyphae (white arrow) penetrating through the root epidermis at 3 hpi. C. Confocal image of lignified root cortex cells with hyphae (white arrow) at 12 hpi. D. Confocal image of root cortex cells demonstrating extensive lignification at 24 hpi. E. Brown necrotic lesions are visible on avocado roots six weeks after Pc inoculation.
Table 1.
Number of differentially expressed avocado transcripts identified according to fold change on the microarray in response to salicylic acid (SA), methyl jasmonate (MeJA) and Phytophthora cinnamomi (Pc).
Fig 2.
SA and JA-linked transcripts induced by P. cinnamomi (Pc) infection of avocado.
Transcripts differentially expressed by either SA of MeJA treatments were identified in P. cinnamomi infected datasets. The values for the transcripts with multiple probes on the microarray was first averaged, and transcripts with poor Pearson correlation was removed. A. The total number of differentially expressed transcripts at 6 hours post treatment/infection. B. The total number of differentially expressed transcripts at 18 hours post treatment/infection. C. The total number of differentially expressed transcripts at 24 hours post treatment/infection. Note that no 24 hrs time point post SA treatment was analyzed.
Fig 3.
HCL performed on fold-change filtered avocado transcripts in the SA (salicylic acid), PC (Phytophthora cinnamomi) and JA (MeJA) datasets.
The colour-scale indicates Log2 fold-change and the branches of the trees are ordered according to the Pearson correlation coefficient (r), with nodes closer to 1 indicative of a positive correlation.
Fig 4.
GO classification differentially expressed avocado transcripts in response to Phytophthora cinnamomi infection.
A) Induced molecular function; B) repressed molecular function; C) induced biological process and D) repressed biological process. Second and third level GO terms are indicated with the corresponding percentage of transcripts for molecular function and biological processes respectively.
Table 2.
Top 25 avocado transcripts differentially regulated by Phytophthora cinnamomi (Pc) at 6 hours post infection.
Table 3.
Top 25 avocado transcripts differentially regulated by Phytophthora cinnamomi (Pc) at 18 hours post infection.
Table 4.
Top 25 avocado transcripts differentially regulated by Phytophthora cinnamomi (Pc) at 24 hours post infection.
Fig 5.
Model of SA and JA pathway temporal regulation induced by Phytophthora cinnamomi in tolerant avocado roots.
At 6 hrs an induction of signaling pathways and transcription factors occurred, which was linked to SA signaling. Subsequently at 18 hrs, both SA and JA-linked induction of ROS, cell wall strengthening and PR transcripts were observed. At 24 hrs transcripts related to lignin formation, flavonoid and volatile compound generation, as well as JA-linked ROS were up regulated. Text shaded in pink are SA-linked, text shaded in green are JA-linked. The pathogen is indicated in grey, nucleus in blue and lignin deposition in maroon.