Impacto del silenciamiento génico de CLAVATA3 y FASCIATED INFLORESCENCE en variedades de tomate de fruto bilocular o multilocular

[ES] La transición floral implica un cambio en la identidad vegetativa del meristemo apical del tallo (SAM), que se transforma en meristemo de inflorescencia, dando lugar a la formación de otros meristemos de inflorescencia secundarios, y estos a su vez se transforman en meristemos florales. En los flancos de los meristemos florales se inicia la formación de los primordios de órganos florales que, tras sucesivos ciclos de división y expansión celular, darán lugar a las flores. Entre los factores que determinan el tamaño final del fruto de tomate se encuentra la tasa de división celular en el meristemo floral, aunque el principal responsable del tamaño final del fruto es el número de carpelos en la flor. Este carácter viene determinado por el tamaño del meristemo floral, cuya regulación implica un mecanismo de retroalimentación negativo en el que juega un papel importante la vía de señalización extracelular formada por los genes CLAVATA (CLV) y WUSCHEL (WUS). El análisis genético de mutantes y los estudios de genética reversa han permitido conocer la base genética y el mecanismo molecular de la ruta CLV/WUS. Así, por ejemplo, mutaciones en los genes CLV conducen a un aumento del tamaño del meristemo floral a través de la expansión de los dominios de expresión de WUS, lo que da lugar a flores con un mayor número de carpelos. En tomate, el fenotipo de ausencia de función del gen FASCIATED INFLORESCENCE (FIN), que codifica una hidroxiprolina O-arabinosiltransferesa, es similar al de los mutantes clavata (clv). En este trabajo de investigación se ha evaluado el impacto del silenciamiento de los genes CLV3 y FIN en dos variedades diferentes de tomate, a saber, Moneymaker y p73, que desarrollan frutos biloculares o multiloculares respectivamente. Para abordar los objetivos del trabajo, previamente se han seleccionado progenies transgénicas de simple copia. Sobre la base del papel que desempeñan estos genes en la regulación de la actividad meristemática, se ha realizado una evaluación in vitro de diferentes caracteres relacionados con la formación de órganos a partir de meristemos. Además, se han evaluado caracteres relacionados con el desarrollo vegetativo y reproductivo en el invernadero. En este sentido, y por lo que respecta al desarrollo vegetativo, el fenotipado se ha centrado en el efecto del silenciamiento sobre la arquitectura de la planta y el desarrollo de órganos foliares. En lo que concierne al desarrollo reproductivo, se ha determinado el efecto del silenciamiento sobre la tasa de cuajado, el calibre y el número de lóculos del fruto y la producción.[EN] Floral transition involves the transformation of stem apical meristem (SAM), which changes its vegetative identity to an inflorescence meristem, also giving rise to secondary inflorescence meristems that finally transform to floral meristems. Primordia of the floral organs start forming on the flanks of floral meristems and after successive division and cellular expansion cycles, they give rise to flowers. Among factors determining final fruit size in tomato, cell division rate it’s included but number of carpels it’s the main accountable for final fruit size. This trait is determined by floral meristem size, whose regulation involves a negative-feedback loop in which the extracellular signalling pathway formed by CLAVATA (CLV) and WUSCHEL (WUS) genes plays a big role. Genetic analysis of mutants and reverse genetics studies have revealed the genetic basis and molecular mechanism of CLAVATA-WUSCHEL pathway. For example, mutations at CLV genes lead to an increase in floral meristem size through WUS expression domains expansion, which gives rise to flowers with larger number of carpels. Tomato mutants lacking function of FASCIATED INFLORESCENCE (FIN) gene, which codifies a hydroxyproline Oarabinosyltransferase, show clv-like phenotypes. In this work, impact of silencing CLV3 and FIN genes on two tomato varieties, Moneymaker and p73, has been evaluated. This varieties develop, respectively, bilocular or multilocular fruits. To address the objectives of this work, single copy transgenic progenies were previously selected. Based on the role played by these genes on meristematic activity regulation, an in vitro evaluation of different traits related to organ formation from meristems has been made. Moreover, traits involved in vegetative and reproductive development have been evaluated at greenhouse. Therefore, for vegetative development, phenotyping has been focused on the effect of silencing on plant architecture and foliar organs development. With respect to reproductive development, the effect of silencing has been evaluated as curdling rate, fruit size, locule number and production.Padilla Herrero, YG. (2019). Impacto del silenciamiento génico de CLAVATA3 y FASCIATED INFLORESCENCE en variedades de tomate de fruto bilocular o multilocular. http://hdl.handle.net/10251/130343TFG

Rootstock-mediated physiological and fruit set responses in pepper under heat stress

An increase in high temperature causes major losses in pepper yields, especially in greenhouses when extending the cropping season to late spring or summer in mild climate areas. Grafting has been identified as a possible tool to cope with this abiotic stress. The objective of this study was to analyze the heat stress impact on a sweet pepper variety grafted onto rootstocks with diverse heat stress tolerances to evaluate high-temperature effects on the leaf metabolism, pollen traits and fruit set. To do so, under two greenhouses conditions (28/22°C and 38/22°C for control and heat stress, respectively), we compared the variety grafted onto two rootstocks (VA/A57 and VA/A55, tolerant and nontolerant, respectively), and used varieties ungrafted (VA) and self-grafted (VA/VA) as controls. VA/A57 obtained the lowest electrolyte leakage, non-disturbed chlorophyll and carotenoids concentration values, increased ascorbic acid and phenols concentrations, and no hydrogen peroxide accumulation. These findings indicate better predisposition to overcome heat stress than other plant combinations. Such physiological responses in leaves conferred by the tolerant rootstock coincided with the highest proline concentration in anthers, and better pollen germination and fruit set compared to the other graft combinations. We conclude that grafting peppers onto a heat stress-tolerant rootstock, such as A57, could overcome negative high-temperature effects better than an ungrafted variety. Moreover, the better physiological performance noted in vegetative parts conferred by a heat stress-tolerant rootstock would also lead to better performance in the reproductive development phase. All this indicates that using tolerant rootstocks in pepper could be an interesting method to alleviate heat stress effects on this crop

Suitable rootstocks can alleviate the effects of heat stress on pepper plants

[EN] In this study, different pepper rootstocks are tested for their ability to overcome heat stress situations. This work aims to evaluate: (i) the physiological mechanisms that occur during long heat stress periods (7 days) under controlled conditions in a pepper variety grafted onto accessions; (ii) the heat stress behaviour of these grafted pepper plants under greenhouse conditions in terms of marketable yields. For this purpose, plants of Lamuyo-type sweet pepper `Herminio F1¿ (VA), grafted onto six accessions (VA/A25, VA/A31, VA/A34, VA/A52, VA/A57, VA/A6), and a self-grafted variety (VA/VA) were grown under controlled conditions in growth chambers (28/24 °C, day/night temperatures and 38/24 °C for control and heat stress, respectively) and under greenhouse conditions (38/24 °C). For the controlled conditions, relative growth rate, leaf area, electrolyte leakage, chlorophyll a fluorescence and heat shock proteins were determined. For the greenhouse conditions, fresh and dry weigh, electrolyte leakage and fruit yield were determined. Our results confirmed that grafting a pepper cultivar onto appropriate rootstocks such as A6, A25 and A57 can overcome the negative effects of heat stress conditions with a higher relative growth rate, leaf area and Fv/Fm, and lower electrolyte leakage under the controlled conditions, and with higher marketable yields under the greenhouse conditions.This work has been financed by the INIA (Spain) and the Spanish Ministry of Science, Innovation and Universities through Project RTA-2017-00030-C02 and the European Regional Development Fund (ERDF) . Ramon Gisbert-Mullor is a beneficiary of a doctoral fellowship (FPU-MEFP (Spain) ) . Yaiza Gara Padilla is a beneficiary of a doctoral fellowship (FPI-INIA (Spain) ) .Gisbert-Mullor, R.; Padilla, YG.; Martínez-Cuenca, M.; López Galarza, SV.; Calatayud, Á. (2021). Suitable rootstocks can alleviate the effects of heat stress on pepper plants. Scientia Horticulturae. 290:1-11. https://doi.org/10.1016/j.scienta.2021.11052911129

Grafting Enhances Pepper Water Stress Tolerance by Improving Photosynthesis and Antioxidant Defense Systems

Currently, limited water supply is a major problem in many parts of the world. Grafting peppers onto adequate rootstocks is a sustainable technique used to cope with water scarcity in plants. For 1 month, this work compared grafted peppers by employing two rootstocks (H92 and H90), with different sensitivities to water stress, and ungrafted plants in biomass, photosynthesis, and antioxidant response terms to identify physiological–antioxidant pathways of water stress tolerance. Water stress significantly stunted growth in all the plant types, although tolerant grafted plants (variety grafted onto H92, Var/H92) had higher leaf area and fresh weight values. Var/H92 showed photosynthesis and stomata conductance maintenance, compared to sensitive grafted plants (Var/H90) and ungrafted plants under water stress, linked with greater instantaneous water use efficiency. The antioxidant system was effective in removing reactive oxygen species (ROS) that could damage photosynthesis; a significant positive and negative linear correlation was observed between the rate of CO2 uptake and ascorbic acid (AsA)/total AsA (AsAt) and proline, respectively. Moreover, in Var/H92 under water stress, both higher proline and ascorbate concentration were observed. Consequently, less membrane lipid peroxidation was quantified in Var/H92

¿Cómo ser una planta de pimiento y sobrevivir a las altas temperaturas?: Tecnología del injerto

En la actualidad, el estrés térmico por altas temperaturas es uno de los factores más importantes que afectan al rendimiento de los cultivos. Esta situación se ve agravada por el escenario de calentamiento global principalmente en la cuenca Mediterránea. En el cultivo forzado de pimiento, este se ve sometido a temperaturas superiores a los 35º C, lo cual impacta negativamente sobre la producción y la calidad de los frutos. La tecnología del injerto en pimiento es una herramienta eficiente para adaptar las variedades al estrés abiótico, principalmente se han realizado estudios sobre la mejora en condiciones de estrés hídrico y salino. Sin embargo, muy pocos estudios se han llevado a cabo sobre la capacidad de los patrones de pimiento en inducir tolerancia a la variedad en condiciones de alta temperatura. En este estudio, siete accesiones de pimiento utilizadas como patrones han sido testadas para estudiar su efecto sobre una variedad de pimiento comercial “Herminio F1” comparando además con la variedad sin injertar

Effect of Grafting on the Production, Physico-Chemical Characteristics and Nutritional Quality of Fruit from Pepper Landraces

Grafting is a widely utilized agronomical technique to improve yield, disease resistance, and quality of fruit and vegetables. This work aims to assess the effect of grafting and fruit ripening on the production, physico-chemical characteristics, and nutritional quality of fruit from Spanish local pepper landraces. Landraces “Cuerno,” “Sueca,” and “Valencia” were used as scions, and “NIBER®” as the rootstock. Two ripening stages of the fruits were sampled: green and red. Grafting improved the yield and marketable quality and did not negatively influence the physico-chemical and nutritional characteristics of the fruit. It was noteworthy that the bioactive compound contents and antioxidant capacity were more related to maturity stage and genotype, and red fruit had a higher antioxidant capacity than green fruit. However, in all the scions, grafting significantly enhanced lycopene content in both red and green fruit. Another important effect of grafting was the volatile compound composition evidenced by discriminant analyses, which was characterized for the first time in the fruit of these landraces. The rootstock and scion combination could be a way to improve not only the production, but also the fruit quality of pepper

New insights into short-term water stress tolerance through transcriptomic and metabolomic analyses on pepper roots

In the current climate change scenario, water stress is a serious threat to limit crop growth and yields. It is necessary to develop tolerant plants that cope with water stress and, for this purpose, tolerance mechanisms should be studied. NIBER® is a proven water stress- and salt-tolerant pepper hybrid rootstock (Gisbert-Mullor et al., 2020; López-Serrano et al., 2020), but tolerance mechanisms remain unclear. In this experiment, NIBER® and A10 (a sensitive pepper accession (Penella et al., 2014)) response to short-term water stress at 5 h and 24 h was studied in terms of gene expression and metabolites content in roots. GO terms and gene expression analyses evidenced constitutive differences in the transcriptomic profile of NIBER® and A10, associated with detoxification systems of reactive oxygen species (ROS). Upon water stress, transcription factors like DREBs and MYC are upregulated and the levels of auxins, abscisic acid and jasmonic acid are increased in NIBER®. NIBER® tolerance mechanisms involve an increase in osmoprotectant sugars (i.e., trehalose, raffinose) and in antioxidants (spermidine), but lower contents of oxidized glutathione compared to A10, which indicates less oxidative damage. Moreover, the gene expression for aquaporins and chaperones is enhanced. These results show the main NIBER® strategies to overcome water stress

Short-term water stress responses of grafted pepper plants are associated with changes in the hormonal balance

Phytohormones play an important role in regulating the plant behavior to drought. In previous studies, NIBER® pepper rootstock showed tolerance to drought in terms of production and fruit quality compared to ungrafted plants. In this study, our hypothesis was that short-term exposure to water stress in young, grafted pepper plants would shed light on tolerance to drought in terms of modulation of the hormonal balance. To validate this hypothesis, fresh weight, water use efficiency (WUE) and the main hormone classes were analyzed in self-grafted pepper plants (variety onto variety, V/V) and variety grafted onto NIBER® (V/N) at 4, 24, and 48h after severe water stress was induced by PEG addition. After 48h, WUE in V/N was higher than in V/V, due to major stomata closure to maintain water retention in the leaves. This can be explained by the higher abscisic acid (ABA) levels observed in the leaves of V/N plants. Despite the interaction between ABA and the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), in relation to stomata closure is controversial, we observed an important increase of ACC at the end of the experiment in V/N plants coinciding with an important rise of the WUE and ABA. The maximum concentration of jasmonic acid and salicylic acid after 48h was found in the leaves of V/N, associated with their role in abiotic stress signaling and tolerance. Respect to auxins and cytokinins, the highest concentrations were linked to water stress and NIBER®, but this effect did not occur for gibberellins. These results show that hormone balance was affected by water stress and rootstock genotype, where NIBER® rootstock displayed a better ability to overcome short-term water stress

A Water Stress–Tolerant Pepper Rootstock Improves the Behavior of Pepper Plants under Deficit Irrigation through Root Biomass Distribution and Physiological Adaptation

The use of rootstocks tolerant to water stress in pepper crops is a complementary technique for saving irrigation water without affecting yields by means of particular rootstock physiological traits, which changes the scion’s perception stress. The present study aimed to analyze the morphological and physiological adaptation of the ‘Cuerno’ pepper cultivar grafted onto tolerant rootstock NIBER® subjected to capacitance sensor-based deficit irrigation. The stomatal conductance, relative water content and leaf water potential parameters were used to confirm the degree of crop stress. Leaf dry weight and root volume were higher in the grafted plants under the control irrigation and stress treatment conditions. Total fresh root biomass and root volume percentage of grafted plants under water stress were 24% and 33% higher, respectively, than the ungrafted plants. The grafted plants subjected to both water stress and control conditions had a higher marketable production than the ungrafted plants. The higher yields obtained using tolerant rootstocks were explained by the reduced blossom-end rot incidence

Grafting onto an Appropriate Rootstock Reduces the Impact on Yield and Quality of Controlled Deficit Irrigated Pepper Crops

In this study, hybrid pepper rootstock NIBER® is tested for its ability to overcome water stress situations under soil conditions. The impact of deficit irrigation (DI) on yield and fruit quality, irrigation water use efficiency is evaluated, and consequently, the agronomic impact of employing water-stress tolerant rootstock is compared to ungrafted pepper plants. For this purpose, plants of the California-type sweet pepper ‘Maestral F1’ grafted onto NIBER® underwent a sustained DI regime during seasons 2018 and 2019 and were compared to their respective controls. Plants were drip-fertirrigated, and volumetric soil water content was continuously monitored by capacitance sensors. Gas exchange and leaf water potential measurements were taken early in the morning and midday 58, 79, and 114 days after transplanting. Plant and fruit dry biomass, marketable quality, blossom-end rot incidence and harvest index were also determined. For consecutive years, our results confirmed that grafting a pepper cultivar onto an appropriate rootstock (NIBER® in this case) as part of a DI strategy can overcome the negative effects of sustained water stress conditions. The plant biomass production and fruit yields of grafted plants were less affected by DI due to less sensitivity to water stress. This can be attributed to a less marked reduction in shoot dry weight in the grafted plants, which allowed greater whole photosynthesis by maintaining sink activity compared to ungrafted plants