Abstract
Jasmonic acid (JA) is a plant hormone that plays important roles in regulating plant defenses against necrotrophic pathogens and herbivorous insects, but the role of JA in mediating the plant responses to root-knot nematodes has been unclear. Here we show that an application of either methyl jasmonate (MeJA) or the JA-mimic coronatine (COR) on Arabidopsis significantly reduced the number of galls caused by the root-knot nematode Meloidogyne hapla. Interestingly, the MeJA-induced resistance was independent of the JA-receptor COI1 (CORONATINE INSENSITIVE 1). The MeJA-treated plants accumulated the JA precursor cis-(+)-12-oxo-phytodienoic acid (OPDA) in addition to JA/JA-Isoleucine, indicating a positive feedback loop in JA biosynthesis. Using mutants in the JA-biosynthetic pathway, we found that plants deficient in the biosynthesis of JA and OPDA were hyper-susceptible to M. hapla. However, the opr3 mutant, which cannot convert OPDA to JA, exhibited wild-type levels of nematode galling. In addition, mutants in the JA-biosynthesis and perception which lie downstream of opr3 also displayed wild-type levels of galling. The data put OPR3 (OPDA reductase 3) as the branch point between hyper-susceptibility and wild-type like levels of disease. Overall, the data suggests that the JA precursor, OPDA, plays a role in regulating plant defense against nematodes.
Highlights
Root-knot nematodes (Meloidogyne sp.) are small soil-borne pathogens that can infect more than 5,000 different plant species and cause significant yield losses (Sasser and Freckman, 1987; Koenning et al, 1999; Trudgill and Blok, 2001)
We wanted to determine if an exogenous application methyl jasmonate (MeJA) can induce resistance to M. hapla in Arabidopsis, and see if this induced resistance was specific to MeJA or if it could be induced by the Jasmonic acid (JA)-analog COR
Since the evidence suggests that oxo-phytodienoic acid (OPDA) is regulating plant susceptibility to nematodes, we explored whether the MeJAinduced resistance in wild-type plants could be linked to elevated OPDA levels
Summary
Root-knot nematodes (Meloidogyne sp.) are small soil-borne pathogens that can infect more than 5,000 different plant species and cause significant yield losses (Sasser and Freckman, 1987; Koenning et al, 1999; Trudgill and Blok, 2001). During feeding site formation, the nematode chooses between 2 and 12 plant cells to pierce with its feeding stylet and induce several rounds of cellular endoreduplication without cytokinesis; the resulting enlarged, multinucleate feedings cells are called giant cells (Williamson and Gleason, 2003; Gheysen and Mitchum, 2011; Role of OPDA in Plant/Root-Knot Nematode Interaction de Almeida Engler and Gheysen, 2013; Perry and Moens, 2013). While the giant cells are forming, the parenchyma cells that surround the giant cells divide, and as a result, large root galls, known as “root knots,” develop in the root systems. Root galling is one of the most obvious disease symptoms resulting from root-knot nematode infection, and it can reflect disease severity
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