Summary• The establishment and development of plant-microorganism interactions involve impressive transcriptomic reprogramming of target plant genes. The symbiont (Sinorhizobium meliloti) and the root knot-nematode pathogen (Meloidogyne incognita) induce the formation of new root organs, the nodule and the gall, respectively.• Using laser-assisted microdissection, we specifically monitored, at the cell level, Medicago gene expression in nodule zone II cells, which are preparing to receive rhizobia, and in gall giant and surrounding cells, which play an essential role in nematode feeding and constitute the typical root swollen structure, respectively.• We revealed an important reprogramming of hormone pathways and C1 metabolism in both interactions, which may play key roles in nodule and gall neoformation, rhizobia endocytosis and nematode feeding. Common functions targeted by rhizobia and nematodes were mainly down-regulated, whereas the specificity of the interaction appeared to involve up-regulated genes.• Our transcriptomic results provide powerful datasets to unravel the mechanisms involved in the accommodation of rhizobia and root-knot nematodes. Moreover, they raise the question of host specificity and the evolution of plant infection mechanisms by a symbiont and a pathogen.
Reported herein is an in vivo triple labelling strategy to monitor the formation of plant cell walls. Based on a combination of copper‐catalysed alkyne–azide cycloaddition (CuAAC), strain‐promoted azide–alkyne cycloaddition (SPAAC), and Diels–Alder reaction with inverse electronic demand (DARinv), this methodology can be applied to various plant species of interest in research. It allowed detection of the differential incorporation of alkynyl‐, azido‐, and methylcyclopropenyl‐tagged reporters of the three main monolignols into de novo biosynthesized lignin in different tissues, cell types, or cell wall layers. In addition, this triple labelling was implemented with different classes of chemical reporters, using two monolignol reporters in conjunction with alkynylfucose to simultaneously monitor the biosynthesis of lignin and non‐cellulosic polysaccharides. This allowed observation of their deposition occurring contemporaneously in the same cell wall.
Summary• Legumes form a symbiotic interaction with bacteria of the Rhizobiaceae family to produce nitrogen-fixing root nodules under nitrogen-limiting conditions. We examined the importance of glutathione (GSH) and homoglutathione (hGSH) during the nitrogen fixation process.• Spatial patterns of the expression of the genes involved in the biosynthesis of both thiols were studied using promoter-GUS fusion analysis. Genetic approaches using the nodule nitrogen-fixing zone-specific nodule cysteine rich (NCR001) promoter were employed to determine the importance of (h)GSH in biological nitrogen fixation (BNF).• The (h)GSH synthesis genes showed a tissue-specific expression pattern in the nodule. Down-regulation of the c-glutamylcysteine synthetase (cECS) gene by RNA interference resulted in significantly lower BNF associated with a significant reduction in the expression of the leghemoglobin and thioredoxin S1 genes. Moreover, this lower (h)GSH content was correlated with a reduction in the nodule size. Conversely, cECS overexpression resulted in an elevated GSH content which was correlated with increased BNF and significantly higher expression of the sucrose synthase-1 and leghemoglobin genes.• Taken together, these data show that the plant (h)GSH content of the nodule nitrogen-fixing zone modulates the efficiency of the BNF process, demonstrating their important role in the regulation of this process.
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