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Rootstocks Overexpressing StNPR1 and StDREB1 Improve Osmotic Stress Tolerance of Wild-Type Scion in Transgrafted Tobacco Plants.

ABSTRACT: In grafted plants, the movement of long-distance signals from rootstocks can modulate the development and function of the scion. To understand the mechanisms by which tolerant rootstocks improve scion responses to osmotic stress (OS) conditions, mRNA transport of osmotic responsive genes (ORGs) was evaluated in a tomato/potato heterograft system. In this system, Solanum tuberosum was used as a rootstock and Solanum lycopersicum as a scion. We detected changes in the gene expression levels of 13 out of the 21 ORGs tested in the osmotically stressed plants; of these, only NPR1 transcripts were transported across the graft union under both normal and OS conditions. Importantly, OS increased the abundance of StNPR1 transcripts in the tomato scion. To examine mRNA mobility in transgrafted plants, StNPR1 and StDREB1 genes representing the mobile and non-mobile transcripts, respectively, were overexpressed in tobacco (Nicotiana tabacum). The evaluation of transgenic tobacco plants indicated that overexpression of these genes enhanced the growth and improved the physiological status of transgenic plants growing under OS conditions induced by NaCl, mannitol and polyethylene glycol (PEG). We also found that transgenic tobacco rootstocks increased the OS tolerance of the WT-scion. Indeed, WT scions on transgenic rootstocks had higher ORGs transcript levels than their counterparts on non-transgenic rootstocks. However, neither StNPR1 nor StDREB1 transcripts were transported from the transgenic rootstock to the wild-type (WT) tobacco scion, suggesting that other long-distance signals downstream these transgenes could have moved across the graft union leading to OS tolerance. Overall, our results signify the importance of StNPR1 and StDREB1 as two anticipated candidates for the development of stress-resilient crops through transgrafting technology.

SUBMITTER: Hezema YS

PROVIDER: S-EPMC8395105 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:IntroductionCitrus productivity has been decreasing in the last decade in the Mediterranean basin as a consequence of climate change and the high levels of salinity found in the aquifers. Citrus varieties are cultivated grafted onto a rootstock, which has been reported as responsible for plant tolerance to adverse situations. However, other important factors for stress tolerance relying in the scion have been less studied. The aim of this study was to evaluate the effect of the grafted scion on citrus tolerance to salt stress.MethodsFour different citrus rootstock/scion combinations were subjected to salt stress for 30 days, using Carrizo citrange (CC) or Citrus macrophylla (CM) as rootstocks, and Navelina orange (NA) or Oronules mandarin (OR) as scions. CM-OR was the most tolerant combination, whereas CC-NA was the most sensitive one.Results and discussionOur results support the idea that the rootstock plays an important role in salt stress tolerance, but scion is also crucial. Thus, photosynthesis and transpiration, processes regulated by abscisic acid and jasmonic acid, are determinant of plant performance. These photosynthetic parameters were not affected in plants of the salt-tolerant combination CM-OR, probably due to the lower intoxication with Cl- ions, allowing a better performance of the photosynthetic machinery under stress conditions. The different stomatal density of the two citrus scions used in this work (higher in the sensitive NA in comparison to the tolerant OR) also contributes to the different tolerance of the grafted plants to this adverse condition. Additionally, CsDTX35.1 and CsDTX35.2, genes codifying for Cl- tonoplast transporters, were exclusively overexpressed in plants of the salt-tolerant combination CM-OR, suggesting that these transporters involved in Cl- compartmentalization could be crucial for salt stress tolerance. It is concluded that to improve citrus tolerance to high salinity, it is important that scions have a versatile photosynthetic system, an adequate stomatal density, and a proper modulation of genes coding for Cl- transporters in the tonoplast.

Project description:Chloroplasts are organelles subjected to extreme oxidative stress conditions. Biomolecules produced in the chloroplasts act as signals guiding plant metabolism toward stress tolerance and play a major role in regulating gene expression in the nucleus. Herein, we used transplastomic plants as an alternative approach to expression of transgenes in the nucleus for conferring stress tolerance to abiotic stresses and herbicides. To investigate the morphophysiological and molecular mechanisms and the role of plastid expressed GSTs in tobacco stress detoxification and stress tolerance, we used transplastomic tobacco lines overexpressing a theta class glutathione transferase (GST) in chloroplasts. The transplastomic plants were tested under drought (0, 100, and 200 mM mannitol) and salinity (0, 150, and 300 mM NaCl) in vitro, and under herbicide stress (Diquat). Our results suggest that pt AtGSTT lines were tolerant to herbicide-induced oxidative and salinity stresses and showed enhanced response tolerance to mannitol-induced osmotic stress compared to WT plants. Overexpression of the Arabidopsis thaliana AtGSTT in the chloroplasts resulted in enhanced photo-tolerance and turgor maintenance under stress. Whole-genome transcriptome analysis revealed that genes related to stress tolerance, were upregulated in pt AtGSTT2a line under both control and high mannitol stress conditions. Transplastomic plants overexpressing the pt AtGSTT2a in the chloroplast showed a state of acclimation to stress, as only limited number of genes were upregulated in the pt AtGSTT2a transplastomic line compared to WT under stress conditions while at the same time genes related to stress tolerance were upregulated in pt AtGSTT2a plants compared to WT in stress-free conditions. In parallel, the metabolic profile indicated limited perturbations of the metabolic homeostasis in the transplastomic lines and greater accumulation of mannitol, and soluble sugars under high mannitol stress. Therefore, transplastomic lines seem to be in a state of acclimation to stress under stress-free conditions, which was maintained even under high mannitol stress. The results help to elucidate the role of GSTs in plant abiotic stress tolerance and the underlying mechanisms of the GSTs expressed in the chloroplast, toward environmental resilience of cultivated crops.

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Rootstocks Overexpressing StNPR1 and StDREB1 Improve Osmotic Stress Tolerance of Wild-Type Scion in Transgrafted Tobacco Plants.

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