Global Gene Expression Profiling During Medicago truncatula–Phymatotrichopsis omnivora Interaction Reveals a Role for Jasmonic Acid, Ethylene, and the Flavonoid Pathway in Disease Development

Abstract

Phymatotrichopsis omnivora (Duggar) Hennebert causes a destructive root rot in cotton, alfalfa (Medicago sativa), and many other dicot species. No consistently effective control measures or resistant host germplasm for Phymatotrichum root rot (PRR) are known. The relative genetic intractability of cotton and alfalfa precludes their use as model pathosystem hosts for P. omnivora. Therefore, we used the model legume M. truncatula and its available genetic and genomic resources to investigate PRR. Confocal imaging of P. omnivora interactions with M. truncatula roots revealed that the mycelia do not form any specialized structures for penetration and mainly colonize cortical cells and, eventually, form a mycelial mantle covering the root's surfaces. Expression profiling of M. truncatula roots infected by P. omnivora identified several upregulated genes, including the pathogenesis-related class I and class IV chitinases and genes involved in reactive oxygen species generation and phytohormone (jasmonic acid and ethylene) signaling. Genes involved in flavonoid biosynthesis were induced (2.5- to 10-fold over mock-inoculated controls) at 3 days postinoculation (dpi) in response to fungal penetration. However, the expression levels of flavonoid biosynthesis genes returned to the basal levels with the progress of the disease at 5 dpi. These transcriptome results, confirmed by real-time quantitative polymerase chain reaction analyses, showed that P. omnivora apparently evades induced host defenses and may downregulate phytochemical defenses at later stages of infection to favor pathogenesis.

Integrated Metabolomics and Transcriptomics Reveal Enhanced Specialized Metabolism in Medicago truncatula Root Border Cells

“…Elevated levels of JA, hexanal (Fig. 8), and transcripts for enzymes in the biosynthetic pathway of these compounds support an important role for border cells in stress metabolism and in protection against pathogen and insect attack, processes in which oxylipins have an established role (Reymond and Farmer, 1998;Uppalapati et al, 2009).…”

“…chip (Uppalapati et al, 2009). Differentially expressed genes from the three different sample types were functionally classified using MapMan categories ( Fig.…”

“…truncatula seedlings were treated with water or a suspension of mycelia from the nonsporulating fungus cotton root rot, a devastating root pathogen that attacks many plants, including legumes Uppalapati et al, 2009Uppalapati et al, , 2010. Border cells and root tips without border cells were collected 24 and 48 h after inoculation and analyzed by UHPLCquadrupole time-of-flight mass spectrometry.…”

Loss of Abaxial Leaf Epicuticular Wax inMedicago truncatula irg1/palm1Mutants Results in Reduced Spore Differentiation of Anthracnose and Nonhost Rust Pathogens

“…Since most of the soybean cultivars and other economically important legumes are susceptible to soybean rust, there is an increasingly urgent demand for identification of durable resistance to soybean rust (van de Mortel et al, 2007). Four single resistance genes to P. pachyrhizi, Rpp1-4, have been described (Hyten et al, 2007;Garcia et al, 2008;Silva et al, 2008;Monteros et al, 2010).…”

Oxylipin-specific cytochrome P450s (CYP74s) inLotus japonicus: their implications in response to mechanical wounding and nodule formation

“…Oxylipin pathway is induced under biotic stresses in leguminous plants. When M. trancatula was infected by pathogenic fungi or by a parasitic plant, the genes for JA synthesis were upregulated (Hiraoka et al 2009;Uppalapati et al 2009;Anderson et al 2010). Aphid infestation resulted in induction of oxylipin pathway through upregulation of LOX and several CYP74 genes in M. trancatula (Gao et al 2007).…”