Open Access
NTRC and thioredoxin f overexpression differentially induces starch accumulation in tobacco leaves
(MDPI, 2019) Ancín Rípodas, María; Larraya Reta, Luis María; Fernández San Millán, Alicia; Veramendi Charola, Jon; Burch Smith, Tessa; Farrán Blanch, Inmaculada; Institute for Multidisciplinary Research in Applied Biology - IMAB
Thioredoxin (Trx) f and NADPH-dependent Trx reductase C (NTRC) have both been proposed as major redox regulators of starch metabolism in chloroplasts. However, little is known regarding the specific role of each protein in this complex mechanism. To shed light on this point, tobacco plants that were genetically engineered to overexpress the NTRC protein from the chloroplast genome were obtained and compared to previously generated Trx f-overexpressing transplastomic plants. Likewise, we investigated the impact of NTRC and Trx f deficiency on starch metabolism by generating Nicotiana benthamiana plants that were silenced for each gene. Our results demonstrated that NTRC overexpression induced enhanced starch accumulation in tobacco leaves, as occurred with Trx f. However, only Trx f silencing leads to a significant decrease in the leaf starch content. Quantitative analysis of enzyme activities related to starch synthesis and degradation were determined in all of the genotypes. Zymographic analyses were additionally performed to compare the amylolytic enzyme profiles of both transplastomic tobacco plants. Our findings indicated that NTRC overexpression promotes the accumulation of transitory leaf starch as a consequence of a diminished starch turnover during the dark period, which seems to be related to a significant reductive activation of ADP-glucose pyrophosphorylase and/or a deactivation of a putative debranching enzyme. On the other hand, increased starch content in Trx f-overexpressing plants was connected to an increase in the capacity of soluble starch synthases during the light period. Taken together, these results suggest that NTRC and the ferredoxin/Trx system play distinct roles in starch turnover.
Open Access
Overexpression of thioredoxin m in tobacco chloroplasts inhibits the protein kinase STN7 and alters photosynthetic performance
(Oxford University Press, 2019) Ancín Rípodas, María; Fernández San Millán, Alicia; Larraya Reta, Luis María; Morales Iribas, Fermín; Veramendi Charola, Jon; Aranjuelo Michelena, Iker; Farrán Blanch, Inmaculada; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua
The activity of the protein kinase STN7, involved in phosphorylation of the light-harvesting complex II (LHCII) proteins, has been reported as being co-operatively regulated by the redox state of the plastoquinone pool and the ferredoxin–thioredoxin (Trx) system. The present study aims to investigate the role of plastid Trxs in STN7 regulation and their impact on photosynthesis. For this purpose, tobacco plants overexpressing Trx f or m from the plastid genome were characterized, demonstrating that only Trx m overexpression was associated with a complete loss of LHCII phosphorylation that did not correlate with decreased STN7 levels. The absence of phosphorylation in Trx m-overexpressing plants impeded migration of LHCII from PSII to PSI, with the concomitant loss of PSI–LHCII complex formation. Consequently, the thylakoid ultrastructure was altered, showing reduced grana stacking. Moreover, the electron transport rate was negatively affected, showing an impact on energy-demanding processes such as the Rubisco maximum carboxylation capacity and ribulose 1,5-bisphosphate regeneration rate values, which caused a strong depletion in net photosynthetic rates. Finally, tobacco plants overexpressing a Trx m mutant lacking the reactive redox site showed equivalent physiological performance to the wild type, indicating that the overexpressed Trx m deactivates STN7 in a redox-dependent way.
Open Access
New in vivo approach to broaden the thioredoxin family interactome in chloroplasts
(MDPI, 2022) Ancín Rípodas, María; Fernández Irigoyen, Joaquín; Santamaría Martínez, Enrique; Larraya Reta, Luis María; Fernández San Millán, Alicia; Veramendi Charola, Jon; Farrán Blanch, Inmaculada; Ciencias de la Salud; Osasun Zientziak; Institute for Multidisciplinary Research in Applied Biology - IMAB
Post-translational redox modifications provide an important mechanism for the control of major cellular processes. Thioredoxins (Trxs), which are key actors in this regulatory mechanism, are ubiquitous proteins that catalyse thiol-disulfide exchange reactions. In chloroplasts, Trx f, Trx m and NADPH-dependent Trx reductase C (NTRC) have been identified as transmitters of the redox signal by transferring electrons to downstream target enzymes. The number of characterised Trx targets has greatly increased in the last few years, but most of them were determined using in vitro procedures lacking isoform specificity. With this background, we have developed a new in vivo approach based on the overexpression of His-tagged single-cysteine mutants of Trx f, Trx m or NTRC into Nicotiana benthamiana plants. The over-expressed mutated Trxs, capable of forming a stable mixed disulfide bond with target proteins in plants, were immobilised on affinity columns packed with Ni-NTA agarose, and the covalently linked targets were eluted with dithiothreitol and identified by mass spectrometry-based proteomics. The in vivo approach allowed identification of 6, 9 and 42 new potential targets for Trx f, Trx m and NTRC, respectively, and an apparent specificity between NTRC and Trxs was achieved. Functional analysis showed that these targets are involved in several cellular processes.
Open Access
Increased bioethanol production from commercial tobacco cultivars overexpressing thioredoxin f grown under field conditions
(Springer, 2014) Farrán Blanch, Inmaculada; Fernández San Millán, Alicia; Ancín Rípodas, María; Larraya Reta, Luis María; Veramendi Charola, Jon; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua
Bioethanol is mainly produced from food crops such as sugar cane and maize while it has been held partly responsible for the rise of food commodity prices. Tobacco, integrated in biorefinery facilities for the extraction of different compounds, could turn into an alternative feedstock for biofuel production. When grown for energy production, using high plant densities and several mowings during the growing season, tobacco can produce large amounts of inexpensive green biomass. We have bred two commercial tobacco cultivars (Virginia Gold and Havana 503B) to increment the carbohydrate content by the overexpression of thioredoxin f in the chloroplast. Marker-free transplastomic plants were rescued and their agronomic performance under field conditions was evaluated. These plants were phenotypically equivalent to their wild types yet showed increased starch (up to 280%) and soluble sugar (up to 74%) contents in leaves relative to their control plants. Fermentable sugars released from the stalk were also higher (up to 24%) for transplastomic plants. After a heat pretreatment, enzymatic hydrolysis and yeast fermentation of leaf and stalk hydrolysates, an average of 20-40% more ethanol was obtained from transplastomic plants in relation to their control wild types. We propose an integral exploitation of the entire tobacco plant managed as a forage crop (harvesting sugar and starch-rich leaves and lignocellulosic stalks) that could considerably cheapen the entire production process.

Ancín Rípodas, María

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