Protection of Sinorhizobium against Host Cysteine-Rich Antimicrobial Peptides Is Critical for Symbiosis

A bacterial membrane protein, BacA, protects Sinorhizobium meliloti against the antimicrobial activity of host peptides, enabling the peptides to induce bacterial persistence rather than bacterial death

(Homo)glutathione Deficiency Impairs Root-knot Nematode Development in Medicago truncatula

Root-knot nematodes (RKN) are obligatory plant parasitic worms that establish and maintain an intimate relationship with their host plants. During a compatible interaction, RKN induce the redifferentiation of root cells into multinucleate and hypertrophied giant cells essential for nematode growth and reproduction. These metabolically active feeding cells constitute the exclusive source of nutrients for the nematode. Detailed analysis of glutathione (GSH) and homoglutathione (hGSH) metabolism demonstrated the importance of these compounds for the success of nematode infection in Medicago truncatula. We reported quantification of GSH and hGSH and gene expression analysis showing that (h)GSH metabolism in neoformed gall organs differs from that in uninfected roots. Depletion of (h)GSH content impaired nematode egg mass formation and modified the sex ratio. In addition, gene expression and metabolomic analyses showed a substantial modification of starch and γ-aminobutyrate metabolism and of malate and glucose content in (h)GSH-depleted galls. Interestingly, these modifications did not occur in (h)GSH-depleted roots. These various results suggest that (h)GSH have a key role in the regulation of giant cell metabolism. The discovery of these specific plant regulatory elements could lead to the development of new pest management strategies against nematodes

REDOX-ACTIVATED EXPRESSION OF THE CYTOSOLIC COPPER-ZINC SUPEROXIDE-DISMUTASE GENE IN NICOTIANA

Superoxide dismutases (SODs; superoxide: superoxide oxidoreductase, EC 1.15.1.1) play a key role in protection against oxygen radicals, and SOD gene expression is highly induced during environmental stress. To determine the conditions of SOD induction, the promoter of the cytosolic copper/zinc SOD (Cu/ZnSODcyt) gene was isolated in Nicotiana plumbaginifolia and fused to the beta-glucuronidase reporter gene. Oxidative stress is likely to alter the cellular redox in favor of the oxidized status. Surprisingly, the expression of the Cu/ZnSODcyt gene is induced by sulfhydryl antioxidants such as reduced glutathione, cysteine, and dithiothreitol, whereas the oxidized forms of glutathione and cysteine have no effect. It is therefore possible that reduced glutathione directly acts as an antioxidant and simultaneously activates the Cu/ZnSODcyt gene during oxidative stress

H2O2 Is Required for Optimal Establishment of the Medicago sativa/Sinorhizobium meliloti Symbiosis▿

The symbiotic interaction between Medicago sativa and Sinorhizobium meliloti RmkatB++ overexpressing the housekeeping catalase katB is delayed, and this delay is combined with an enlargement of infection threads. This result provides evidence that H2O2 is required for optimal progression of infection threads through the root hairs and plant cell layers

Differential expression of CuZn- and Fe-superoxide dismutase genes of tobacco during development, oxidative stress, and hormonal treatments

Chloroplasts of Nicotiana tabacum have two superoxide dismutases: a Fe- and a CuZn-containing enzyme, encoded by the nuclear genes sodB and sodCp, respectively, As a first step in studying the physiological function of these two enzymes, we compared the expression of sodB and sodCp in different plant organs, in response to hormonal treatments, and upon treatment with paraquat and Norflurazon. The sodCp transcript and active enzyme were detected only in young leaves of mature plants. The sodB transcript was more abundant in young compared to old leaves, but the enzymatic activity was higher in mature and senescent leaves. sodCp and sodB exhibited a different expression pattern upon treatment with abscisic acid, indole-3-acetic acid, kinetin, gibberellin, and 1-aminocyclopropane-1-carboxylate. Paraquat treatment caused a decrease in abundance of both transcripts, although the dose dependency of this decrease differed, Norflurazon-induced photooxidation resulted in a 10-fold increase of sodCp mRNA whereas the sodB transcript level was 25% higher than the control, These differences in expression might explain why both plastid-located superoxide dismutase enzymes are needed, particularly under stress conditions

Differential expression of CuZn-and Fe-superoxide dismutase genes of tobacco during development, oxidative stress, and hormonal treatments

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