Terpenoid and lipid profiles vary in different Phytophthora cactorum-strawberry interactions

Specialized metabolites are essential components in plant defence systems, serving as signalling molecules and chemical weapons against pathogens. The manipulation of plant defence metabolome or metabolites can thus be an important virulence strategy for pathogens. Because of their central role, metabolites can give valuable insights into plant-pathogen interactions. Here, we have conducted nontargeted metabolite profiling with UPLCESI-qTOF-MS to investigate the metabolic changes that have taken place in the crown tissue of Fragaria vesca L. (woodland strawberry) and Fragaria x ananassa (Weston) Duchesne ex Rozier (garden strawberry) during 48 h after Phytophthora cactorum challenge. Two P. cactorum isolates were compared: Pc407 is highly virulent to F. x ananassa and causes crown rot, whereas Pc440 is mildly virulent. In total, 45 metabolites differentially accumulated between the treatment groups were tentatively identified. Triterpenoids and various lipid compounds were highly represented. The levels of several triterpenoids increased upon inoculation, some of them showing distinct accumulation patterns in different interactions. Triterpenoids could either inhibit or stimulate P. cactorum growth and, therefore, triterpenoid profiles might have significant impact on disease progression. Of the lipid compounds, lysophospholipids, linoleic acid and linolenic acid were highly accumulated in the most compatible Pc407 - F. x ananassa interaction. As lysophospholipids promote cell death and have been linked to susceptibility, these compounds might be involved in the pathogenesis of crown rot disease. This metabolite analysis revealed potential factors contributing to the outcome of P. cactorum - strawberry interactions. The information is highly valuable, as it can help to find new breeding strategies and new solutions to control P. cactorum in strawberry

Non-invasive assessment and visualization of Phytophthora cactorum infection in strawberry crowns using quantitative magnetic resonance imaging

Abstract Phytophthora cactorum is an oomycete species that causes enormous losses on horticultural crops, including strawberries. The purpose of this work was to investigate the alterations caused by P. cactorum inoculation in hydroponically grown strawberry plantlets (Fragaria × ananassa Duch.) using quantitative magnetic resonance imaging (qMRI). It was observed that with MRI, spatial and temporal progression of the infection could be observed in the crown using quantitative MR parameters, namely relaxation time maps. Relaxation times are numeric subject-specific properties that describe the MR signal behavior in an examined anatomical region. Elevated $$T_{2}$$ T 2 relaxation time values were observed inside the infected plant crowns with respect to the healthy references. The $$T_{2}$$ T 2 and $$T_{2}^{*}$$ T 2 ∗ values of healthy plants were small in the crown region and further diminished during the development of the plant. Furthermore, elevated $$T_{1}$$ T 1 relaxation time values were seen in regions where P. cactorum progression was observed in corresponding plant dissection photographs. Quantitative susceptibility maps (QSM) were calculated to estimate the local magnetic field inhomogeneities. The QSM suggests magnetic susceptibility differences near the center of the pith. This study provides novel non-invasive information on the structure and development of strawberry plants and the effects caused by the P. cactorum infection

Reprogramming of Strawberry (<i>Fragaria vesca</i>) Root Transcriptome in Response to <i>Phytophthora cactorum</i>

<div><p>Crown rot (<i>Phytophthora cactorum</i>) causes significant economic losses in strawberry production. The best control strategy would be to use resistant cultivars, but polygenically inherited resistance makes the breeding of the garden strawberry (<i>Fragaria</i> × <i>ananassa</i>) challenging. The diploid wild strawberry <i>Fragaria vesca</i> Hawaii 4 genotype was shown previously to have resistance against crown rot. To explore the resistance mechanisms, we inoculated the roots of Hawaii 4 with <i>P</i>. <i>cactorum</i> in a novel <i>in vitro</i> hydroponic system to minimize interference caused by other microbes. Major reprogramming of the root transcriptome occurred, involving 30% of the genes. The surveillance system of the plant shifted from the development mode to the defense mode. Furthermore, the immune responses as well as many genes involved in the biosynthesis of the defense hormones jasmonic acid, ethylene and salicylic acid were up-regulated. Several major allergen-like genes encoding PR-10 proteins were highly expressed in the inoculated plants, suggesting that they also have a crucial role in the defense responses against <i>P</i>. <i>cactorum</i>. Additionally, flavonoids and terpenoids may be of vital importance, as several genes involved in their biosynthesis were up-regulated. The cell wall biosynthesis and developmental processes were down-regulated, possibly as a result of the down-regulation of the key genes involved in the biosynthesis of growth-promoting hormones brassinosteroids and auxin. Of particular interest was the expression of potential resistance genes in the recently identified <i>P</i>. <i>cactorum</i> resistance locus <i>RPc-1</i>. These new findings help to target the breeding efforts aiming at more resistant strawberry cultivars.</p></div

Genes in <i>P</i>. <i>cactorum</i> resistance locus <i>RPc-1</i> expressed in the roots of <i>F</i>. <i>vesca</i>.

<p>Genes in <i>P</i>. <i>cactorum</i> resistance locus <i>RPc-1</i> expressed in the roots of <i>F</i>. <i>vesca</i>.</p

Effect of <i>P</i>. <i>cactorum</i> inoculation of <i>F</i>. <i>vesca</i> roots on the expression of genes involved in cell wall synthesis.

<p>Effect of <i>P</i>. <i>cactorum</i> inoculation of <i>F</i>. <i>vesca</i> roots on the expression of genes involved in cell wall synthesis.</p

<i>P</i>. <i>cactorum</i> inoculation changes isoprenoid metabolism in <i>F</i>. <i>vesca</i> roots.

<p>Several genes involved in MVA pathway were up-regulated, whereas none of the MEP pathway genes were up-regulated. Products of the MVA pathway appear to be targeted to sesquiterpenoid and triterpenoid biosynthesis rather than to sterol biosynthesis. AACT, acetoacetyl-CoA thiolase; HMGS, 3-hydroxy-3-methylglutaryl-CoA synthase; HMGR, 3-hydroxy-3-methylglutaryl-CoA reductase; MVK, mevalonate kinase; PMK, phosphomevalonate kinase; MPDC, diphosphomevalonate decarboxylase; IDI, isopentenyl-diphosphate Delta-isomerase; DXS, 1-deoxy-D-xylulose-5-phosphate synthase; DXR, 1-deoxy-D-xylulose 5-phosphate reductoisomerase; MCT, 2-C-methyl-D-erythritol 4-phosphate cytidyltransferase; CMK, 4-(cytidine 5’-diphospho)-2-C-methyl-D-erythritol kinase; MDS, 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase; HDS, 1-hydroxy-2-methyl-2-butenyl 4-diphosphate synthase; HDR, 1-hydroxy-2-methyl-2-butenyl 4-diphosphate reductase; FPS, farnesyl diphosphate synthase; GPPS, geranyl diphosphate synthase; GGPPS, geranylgeranyl diphosphate synthase; SQS, squalene synthase; SQE, squalene epoxidase; GDS, (-)-germacrene D synthase-like; BAS, beta-amyrin synthase-like; CAS, cycloartenol synthase -like; APS, (-)-alpha-pinene synthase-like.</p

Summary of RNA sequencing results.

<p>Controls 1 to 3 refer to water control replicates, inoculated 1 to 3 to replicate plants inoculated with <i>P</i>. <i>cactorum</i> 407; each replicate represents roots collected from one individual plant.</p

Receptor-like kinases expressed in the wild strawberry <i>F</i>. <i>vesca</i>.

<p>Receptor-like kinases expressed in the wild strawberry <i>F</i>. <i>vesca</i>.</p