Natural genetic variation and negative density effects in plant-nematode interactions.

Arabidopsis thaliana is a suitable host for phytoparasitic nematodes of the genus Meloidogyne. Successful nematode infection leads to the formation of root galls. We tested for natural genetic variation and inoculation density effects on nematode reproductive success in the interaction between A. thaliana and Meloidogyne javanica. We inoculated different Arabidopsis genotypes with two sources of nematodes at two different doses, using a mild protocol for inoculum preparation. We counted root galls and egg masses 2 months after inoculation. We obtained a high number of successful nematode infections. Infection success differed among Arabidopsis genotypes in interaction with the nematode source. Overall, infection success and reproductive success of nematodes were lower at a higher inoculum dose of nematodes. Our results indicate that natural genetic variation in both host plants and nematodes, as well as short- and long-term negative density effects, shape nematode reproductive success.

[Biosynthesis of indole glucosinolates and ecological role of secondary modification pathways]. / Biosynthèse des glucosinolates indoliques et rôle écologique de leurs modifications secondaires.

Indole glucosinolates are plant secondary metabolites derived from the amino acid tryptophan. They are part of a large group of sulfur-containing molecules almost exclusively found among Brassicales, which include the mustard family (Brassicaceae) with many edible plant species of major nutritional importance. These compounds mediate numerous interactions between these plants and their natural enemies and are therefore of major biological and economical interest. This literature review aims at taking stock of recent advances of our knowledge about the biosynthetic pathways of indole glucosinolates, but also about the defense strategies and ecological processes involving these metabolites.

Methyl Transfer in Glucosinolate Biosynthesis Mediated by Indole Glucosinolate O-Methyltransferase 5.

Indole glucosinolates (IGs) are plant secondary metabolites that are derived from the amino acid tryptophan. The product of Arabidopsis (Arabidopsis thaliana) IG core biosynthesis, indol-3-ylmethyl glucosinolate (I3M), can be modified by hydroxylation and subsequent methoxylation of the indole ring in position 1 (1-IG modification) or 4 (4-IG modification). Products of the 4-IG modification pathway mediate plant-enemy interactions and are particularly important for Arabidopsis innate immunity. While CYP81Fs encoding cytochrome P450 monooxygenases and IGMTs encoding indole glucosinolate O-methyltransferases have been identified as key genes for IG modification, our knowledge about the IG modification pathways is not complete. In particular, it is unknown which enzyme is responsible for methyl transfer in the 1-IG modification pathway and whether this pathway plays a role in defense, similar to 4-IG modification. Here, we analyze two Arabidopsis transfer DNA insertion lines with targeted metabolomics. We show that biosynthesis of 1-methoxyindol-3-ylmethyl glucosinolate (1MOI3M) from I3M involves the predicted unstable intermediate 1-hydroxyindol-3-ylmethyl glucosinolate (1OHI3M) and that IGMT5, a gene with moderate similarity to previously characterized IGMTs, encodes the methyltransferase that is responsible for the conversion of 1OHI3M to 1MOI3M. Disruption of IGMT5 function increases resistance against the root-knot nematode Meloidogyne javanica and suggests a potential role for the 1-IG modification pathway in Arabidopsis belowground defense.