Exposure of Arabidopsis (Arabidopsis thaliana) to 4 °C imprints a cold memory that modulates gene expression in response to a second (triggering) stress stimulus applied several days later. Comparison of plastid transcriptomes of cold-primed and control plants directly before they were exposed to the triggering stimulus showed downregulation of several subunits of chloroplast NADPH dehydrogenase (NDH) and regulatory subunits of ATP synthase. NDH is, like PGR5-PGRL1 (Proton gradient 5–PGR5-like1), a thylakoid-embedded, ferredoxin-dependent plastoquinone reductase that protects photosystem I and stabilizes ATP synthesis by cyclic electron transport. Like PGRL1A and PGRL1B transcript levels, ndhA and ndhD transcript levels decreased during the 24 h long priming cold treatment. PGRL1 transcript levels were quickly reset in the post-cold phase, but expression of ndhA remained low. The transcript abundances of other ndh genes decreased within the next days. Comparison of tAPX-free and transiently tAPX-overexpressing or tAPX-downregulating Arabidopsis lines demonstrated that ndh expression is suppressed by post-cold induction of thylakoid-bound ascorbate peroxidase (tAPX). Four days after cold-priming, when tAPX protein accumulation was maximal, NDH activity was almost fully lost. Lack of the NdhH-folding chaperonin Crr27 (Cpn60β4), but not lack of the NDH activity modulating subunits NdhM, NdhO, or PnsB2 (Photosynthetic NDH subcomplex B2), strengthened priming regulation of ZAT10 (Zinc finger of Arabidopsis thaliana 10), which is a nuclear-localized target gene of the tAPX-dependent cold-priming pathway. We conclude that cold-priming modifies chloroplast-to-nucleus stress signalling by tAPX-mediated suppression of NDH-dependent cyclic electron transport and that plastid encoded NdhH, which controls subcomplex A assembly, is of special importance for memory stabilization.

SummaryMolecular aspects of the responses of tomato (Solanum lycopersicum) plants to invasion by Meloidogyne incognita, as well as the nematode reproduction capacity, were investigated and the role of jasmonic acid (JA) in these interactions was evaluated. Real-time quantitative PCR analysis showed that resistant and susceptible plants had similar levels of Mi1.2, PR1 and PR6 gene expression in stress-free conditions. During nematode invasion resistant plants showed up-regulation of Mi1.2, PR1 and PR6 genes and no reproduction of M. incognita. By contrast, susceptible plants showed no response in gene expression and the nematode had a high level of reproduction. Treatment of tomato plants with JA modulated Mi1.2 and PR6 gene expression that was accompanied by a suppression of the M. incognita reproduction on the roots of JA-treated susceptible plants.

Abstract— The expression of the genes encoding the inhibitors of serine (ISP) and cysteine ​​proteinases (ICP) was studied in the roots of tomato plants resistant and susceptible to the root-knot nematode Meloidogyne incognita during infection and under the effects of signaling molecules: salicylic (SA) and jasmonic (JA) acids. It was shown that, upon infection, resistant plants are characterized by an increased accumulation of transcripts of the ICP and ISP genes at the stages of penetration and development in the roots, while the level of transcription does not change in susceptible plants. There was a significant decrease in nematode invasion in susceptible plants after treatment with SA or JA compared to untreated plants, which makes it possible to determine the role of the studied proteinase inhibitors in resistance induced by signaling molecules. It was revealed that an increase in expression of the genes of proteinase inhibitors is accompanied by inhibition of the reproductive potential and size of M. incognita females, as well as by a decrease in plant infection.