Project description:Phytophthora cinnamomi Rands (Pc) is a hemibiotrophic oomycete and the causal agent of Phytophthora root rot (PRR) of the commercially important fruit crop avocado (Persea americana Mill.). Plant defense against pathogens is modulated by phytohormone signaling pathways such as salicylic acid (SA), jasmonic acid (JA), ethylene (ET), auxin and abscisic acid. The role of specific signaling pathways induced and regulated during hemibiotroph-plant interactions has been widely debated. Some studies report SA mediated defense while others hypothesize that JA responses restrict the spread of pathogens. This study aimed to identify the role of SA- and JA- associated genes in the defense strategy of a resistant avocado rootstock, Dusa® in response to Pc infection. Transcripts associated with SA-mediated defense pathways and lignin biosynthesis were upregulated at 6 hours post-inoculation (hpi). Results suggest that auxin, reactive oxygen species (ROS) and Ca2+ signaling was also important during this early time point, while JA signaling was absent. Both SA and JA defense responses were shown to play a role during defense at 18 hpi. Induction of genes associated with ROS detoxification and cell wall digestion (β-1-3-glucanase) was also observed. Most genes induced at 24 hpi were linked to JA responses. Other processes at play in avocado at 24 hpi include cell wall strengthening, the formation of phenolics and induction of arabinogalactan, a gene linked to Pc zoospore immobility. This study represents the first transcriptome wide analysis of a resistant avocado rootstock treated with SA and JA compared to Pc infection. The results provide evidence of a biphasic defense response against the hemibiotroph, which initially involves SA-mediated gene expression followed by the enrichment of JA-mediated defense from 18 to 24 hpi. Genes and molecular pathways linked to Pc resistance are highlighted and may serve as future targets for manipulation in the development of PRR resistant avocado rootstocks.
Project description:Current understanding of floral developmental genetics comes primarily from the core-eudicot model Arabidopsis thaliana. Here we explore the floral transcriptome of the basal angiosperm, Nuphar advena (water lily), for insights into the ancestral developmental program of flowers. Several thousand Nuphar genes with significantly up-regulated floral expression are identified, including homologs of the well-known ABCE floral regulators. However, strong similarities in the expression profiles of different organ categories contradict the organ-specific spatial expression domains predicted by the ABCE model. The broadly overlapping transcriptional programs observed among floral organs in Nuphar are shared with the magnoliid Persea americana (avocado), supporting the inference that this is the ancestral condition in angiosperms. Consequently, the predominantly organ-specific transcriptional programs that characterize Arabidopsis flowers (and perhaps other eudicots) are derived. The transcriptional landscapes in Arabidopsis correlate with a shift toward morphologically distinct floral organs, including differentiated sepals and petals, and a perianth distinct from stamens and carpels. In contrast to most eudicots, perianth organs are weakly differentiated in Nuphar and Persea, with staminodial intermediates between stamens and perianth in Nuphar, and between stamens and carpels in Persea. Our findings suggest that genetic regulation of more spatially discrete transcriptional programs underlies the evolution of floral morphology. Custom microarrays targeting 6,220 unique Nuphar floral transcripts were used to measure expression levels in eight tissues using an interwoven double-loop design for 16 arrays.
Project description:Current understanding of floral developmental genetics comes primarily from the core-eudicot model Arabidopsis thaliana. Here we explore the floral transcriptome of the basal angiosperm, Nuphar advena (water lily), for insights into the ancestral developmental program of flowers. Several thousand Nuphar genes with significantly up-regulated floral expression are identified, including homologs of the well-known ABCE floral regulators. However, strong similarities in the expression profiles of different organ categories contradict the organ-specific spatial expression domains predicted by the ABCE model. The broadly overlapping transcriptional programs observed among floral organs in Nuphar are shared with the magnoliid Persea americana (avocado), supporting the inference that this is the ancestral condition in angiosperms. Consequently, the predominantly organ-specific transcriptional programs that characterize Arabidopsis flowers (and perhaps other eudicots) are derived. The transcriptional landscapes in Arabidopsis correlate with a shift toward morphologically distinct floral organs, including differentiated sepals and petals, and a perianth distinct from stamens and carpels. In contrast to most eudicots, perianth organs are weakly differentiated in Nuphar and Persea, with staminodial intermediates between stamens and perianth in Nuphar, and between stamens and carpels in Persea. Our findings suggest that genetic regulation of more spatially discrete transcriptional programs underlies the evolution of floral morphology.
Project description:White root rot disease caused by Rosellinia necatrix is one of the most important pathogens affecting avocado productivity in temperate, tropical and subtropical climates. Control of this disease is complex and nowadays, lies in the use of physical and chemical methods, although none have proven to be fully effective. Detailed understanding of the molecular mechanisms underlying white root rot disease has the potential of aiding future developments in disease resistance and management. In this regard, this study used RNAseq technology to compare the transcriptomic profiles of R. necatrix during infection of susceptible avocado `Dusa´ roots with that obtained from the fungus cultured in rich medium. The transcriptomes from three biological replicates of R. necatrix colonizing avocado roots (RC) and R. necatrix growing on potato dextrose agar media (PDA) were obtained using Illumina sequencing. A total of 12,104 transcripts were obtained, among which 1937 were differentially expressed genes (DEG), 137 exclusively expressed in RC and 160 and PDA. Interestingly genes involved in the production of fungal toxins, detoxification of toxic compounds, hormone biosynthesis, gene silencing and plant cell wall degradation were overexpressed during the infection process. In addition, 23 out of the 137 contigs, only expressed during R. necatrix growth on avocado roots, were predicted as candidate effector proteins (CEP) by the CSIRO tool with a probability above 60%. The PHI (Pathogen Host Interaction) database revealed that 11 R. necatrix CEP were previously annotated as effectors genes proven experimentally via pathogen-host interaction.
Project description:The aim of this study was to evaluate the physiological response and the expression analysis of `Dusa´ avocado rootstocks subjected to two different levels of water stress, and their subsequent recovery. At the beginning of the experiment, avocado plants were divided in Control plants (watered to field capacity (Fc) throughout the experiment) and stressed plants that were subjected to controlled substrate drying-up until they reached 50% of Fc (mild-WS) and 25% of Fc (severe-WS), respectively. Afterwards, plants were fully irrigated to assess drought recovery response. A set of physiological measurement were taken at leaf and whole-plant levels to assess avocado response to each level of water stress and rewatering. Root samples were collected in mild-WS and severe-WS and gene expression analysis was carried out using a targeted cDNA avocado stress microarray containing transcripts from de novo sequencing of 'Dusa' in response to biotic and abiotic stress. Avocado gene expression profiles under different levels of water stress are discussed in order to shed light on the molecular mechanisms associated with water deprivation in Dusa avocado rootstocks.