An insertional mutagenesis programme with an enhancer trap for the identification and tagging of genes involved in abiotic stress tolerance in the tomato wild-related species Solanum pennellii

Loss of function mutations at the tomato SSI2 locus impair plant growth and development by altering the fatty acid desaturation pathway

The stearoyl-ACP desaturase (SACPD) is a key enzyme in the regulation of saturated to unsaturated fatty acid ratio, playing a crucial role in regulating membrane stability and fluidity, as well as photosynthesis efficiency, which makes it an important research focus in crop species. This study reports the characterization and molecular cloning of pale dwarf (pad), a new tomato (Solanum lycopersicum L.) T-DNA recessive mutant, which exhibits a dwarf and chlorotic phenotype. Functional studies of the T-DNA tagged gene were conducted, including phylogenetic analysis, expression and metabolomic analyses, and generation of CRISPR/Cas9 knockout lines. The cloning of T-DNA flanking genomic sequences and a co-segregation analysis found the pad phenotype was caused by a T-DNA insertion disrupting the tomato homologue of the Arabidopsis SUPPRESSOR OF SALICYLIC ACID INSENSITIVITY 2 (SlSSI2), encoding a plastid localized isoform of SACPD. The phenotype of CRISPR/Cas9 SlSSI2 knockout lines confirmed that the morphological abnormalities in pad plants were due to SlSSI2 loss of function. Functional, metabolomic and expression analyses proved that SlSSI2 disruption causes deficiencies in 18:1 fatty acid desaturation and leads to diminished jasmonic acid (JA) content and increased salicylic acid (SA) levels. Overall, these results proved that SSI2 plays a crucial role in the regulation of polyunsaturated fatty acid profiles in tomato, and revealed that SlSSI2 loss of function results in an inhibited JA-responsive signalling pathway and a constitutively activated SA-mediated defence signalling response. This study lays the foundation for further research on tomato SACPDs and their role in plant performance and fitness.

Mutagenesis-based plant breeding approaches and genome engineering: A review focused on tomato

Breeding is the most important and efficient method for crop improvement involving repeated modification of the genetic makeup of a plant population over many generations. In this review, various accessible breeding approaches, such as conventional breeding and mutation breeding (physical and chemical mutagenesis and insertional mutagenesis), are discussed with respect to the actual impact of research on the economic improvement of tomato agriculture. Tomatoes are among the most economically important fruit crops consumed worldwide because of their high nutritional content and health-related benefits. Additionally, we summarize mutation-based mapping approaches, including Mutmap and MutChromeSeq, for the efficient mapping of several genes identified by random indel mutations that are beneficial for crop improvement. Difficulties and challenges in the adaptation of new genome editing techniques that provide opportunities to demonstrate precise mutations are also addressed. Lastly, this review focuses on various effective and convenient genome editing tools, such as RNA interference (RNAi), zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeats (CRISPR/Cas9), and their potential for the improvement of numerous desirable traits to allow the development of better varieties of tomato and other horticultural crops.

Multitraits evaluation of a Solanum pennellii introgression tomato line challenged by combined abiotic stress

Rising daily temperatures and water shortage are two of the major concerns in agriculture. In this work, we analysed the tolerance traits in a tomato line carrying a small region of the Solanum pennellii wild genome (IL12-4-SL) when grown under prolonged conditions of single and combined high temperature and water stress. When exposed to stress, IL12-4-SL showed higher heat tolerance than the cultivated line M82 at morphological, physiological, and biochemical levels. Moreover, under stress IL12-4-SL produced more flowers than M82, also characterized by higher pollen viability. In both lines, water stress negatively affected photosynthesis more than heat alone, whereas the combined stress did not further exacerbate the negative impacts of drought on this trait. Despite an observed decrease in carbon fixation, the quantum yield of PSII linear electron transport in IL12-4-SL was not affected by stress, thereby indicating that photochemical processes other than CO₂ fixation acted to maintain the electron chain in oxidized state and prevent photodamage. The ability of IL12-4-SL to tolerate abiotic stress was also related to the intrinsic ability of this line to accumulate ascorbic acid. The data collected in this study clearly indicate improved tolerance to single and combined abiotic stress for IL12-4-SL, making this line a promising one for cultivation in a climate scenario characterized by frequent and long-lasting heatwaves and low rainfall.

Application of Genome Editing in Tomato Breeding: Mechanisms, Advances, and Prospects

Plants regularly face the changing climatic conditions that cause biotic and abiotic stress responses. The abiotic stresses are the primary constraints affecting crop yield and nutritional quality in many crop plants. The advances in genome sequencing and high-throughput approaches have enabled the researchers to use genome editing tools for the functional characterization of many genes useful for crop improvement. The present review focuses on the genome editing tools for improving many traits such as disease resistance, abiotic stress tolerance, yield, quality, and nutritional aspects of tomato. Many candidate genes conferring tolerance to abiotic stresses such as heat, cold, drought, and salinity stress have been successfully manipulated by gene modification and editing techniques such as RNA interference, insertional mutagenesis, and clustered regularly interspaced short palindromic repeat (CRISPR/Cas9). In this regard, the genome editing tools such as CRISPR/Cas9, which is a fast and efficient technology that can be exploited to explore the genetic resources for the improvement of tomato and other crop plants in terms of stress tolerance and nutritional quality. The review presents examples of gene editing responsible for conferring both biotic and abiotic stresses in tomato simultaneously. The literature on using this powerful technology to improve fruit quality, yield, and nutritional aspects in tomato is highlighted. Finally, the prospects and challenges of genome editing, public and political acceptance in tomato are discussed.

Approaching the genetic dissection of indirect adventitious organogenesis process in tomato explants

The screening of 862 T-DNA lines was carried out to approach the genetic dissection of indirect adventitious organogenesis in tomato. Several mutants defective in different phases of adventitious organogenesis, namely callus growth (tdc-1), bud differentiation (tdb-1, -2, -3) and shoot-bud development (tds-1) were identified and characterized. The alteration of the TDC-1 gene blocked callus proliferation depending on the composition of growth regulators in the culture medium. Calli from tds-1 explants differentiated buds but did not develop normal shoots. Histological analysis showed that their abnormal development is due to failure in the organization of normal adventitious shoot meristems. Interestingly, tdc-1 and tds-1 mutant plants were indistinguishable from WT ones, indicating that the respective altered genes play specific roles in cell proliferation from explant cut zones (TDC-1 gene) or in the organization of adventitious shoot meristems (TDS-1 gene). Unlike the previous, plants of the three mutants defective in the differentiation of adventitious shoot-buds (tdb-1, -2, -3) showed multiple changes in vegetative and reproductive traits. Cosegregation analyses revealed the existence of an association between the phenotype of the tdb-3 mutant and a T-DNA insert, which led to the discovery that the SlMAPKKK17 gene is involved in the shoot-bud differentiation process.

Genome-wide assessment of population structure and genetic diversity of Chinese Lou onion using specific length amplified fragment (SLAF) sequencing

Lou onion (Allium fistulosum L. var. viviparum) is an abundant source of flavonols which provides additional health benefits to diseases. Genome-wide specific length amplified fragment (SLAF) sequencing method is a rapidly developed deep sequencing technologies used for selection and identification of genetic loci or markers. This study aimed to elucidate the genetic diversity of 122 onion accessions in China using the SLAF-seq method. A set of 122 onion accessions including 107 A.fistulosum L. var. viviparum Makino, 3 A.fistulosum L. var. gigantum Makino, 3 A.mongolicum Regel and 9 A.cepa L. accessions (3 whites, 3 reds and 3 yellows) from different regions in China were enrolled. Genomic DNA was isolated from young leaves and prepared for the SLAF-seq, which generated a total of 1,387.55 M reads and 162,321 high quality SNPs (integrity >0.5 and MAF >0.05). These SNPs were used for the construction of neighbor-joining phylogenetic tree, in which 10 A.fistulosum L. var. viviparum Makino accessions from Yinchuan (Ningxia province) and Datong (Qinghai province) had close genetic relationship. The 3 A.cepa L. clusters (red, white and yellow) had close genetic relationship especially with the 97 A.fistulosum L. var. viviparum Makino accessions. Population structure analysis suggested entire population could be clustered into 3 groups, while principal component analysis (PCA) showed there were 4 genetic groups. We confirmed the SLAF-seq approach was effective in genetic diversity analysis in red onion accessions. The key findings would provide a reference to the Lou onion germplasm in China.

Phenotypic and genetic characterization of tomato mutants provides new insights into leaf development and its relationship to agronomic traits

BACKGROUND

Tomato mutants altered in leaf morphology are usually identified in the greenhouse, which demands considerable time and space and can only be performed in adequate periods. For a faster but equally reliable scrutiny method we addressed the screening in vitro of 971 T-DNA lines. Leaf development was evaluated in vitro in seedlings and shoot-derived axenic plants. New mutants were characterized in the greenhouse to establish the relationship between in vitro and in vivo leaf morphology, and to shed light on possible links between leaf development and agronomic traits, a promising field in which much remains to be discovered.

RESULTS

Following the screening in vitro of tomato T-DNA lines, putative mutants altered in leaf morphology were evaluated in the greenhouse. The comparison of results in both conditions indicated a general phenotypic correspondence, showing that in vitro culture is a reliable system for finding mutants altered in leaf development. Apart from providing homogeneous conditions, the main advantage of screening in vitro lies in the enormous time and space saving. Studies on the association between phenotype and nptII gene expression showed co-segregation in two lines (P > 99%). The use of an enhancer trap also allowed identifying gain-of-function mutants through reporter expression analysis. These studies suggested that genes altered in three other mutants were T-DNA tagged. New mutants putatively altered in brassinosteroid synthesis or perception, mutations determining multiple pleiotropic effects, lines affected in organ curvature, and the first tomato mutant with helical growth were discovered. Results also revealed new possible links between leaf development and agronomic traits, such as axillary branching, flower abscission, fruit development and fruit cracking. Furthermore, we found that the gene tagged in mutant 2635-MM encodes a Sterol 3-beta-glucosyltransferase. Expression analysis suggested that abnormal leaf development might be due to the lack-off-function of this gene.

CONCLUSION

In vitro culture is a quick, efficient and reliable tool for identifying tomato mutants altered in leaf morphology. The characterization of new mutants in vivo revealed new links between leaf development and some agronomic traits. Moreover, the possible implication of a gene encoding a Sterol 3-beta-glucosyltransferase in tomato leaf development is reported.

Developmental role of the tomato Mediator complex subunit MED18 in pollen ontogeny

Pollen development is a crucial step in higher plants, which not only makes possible plant fertilization and seed formation, but also determines fruit quality and yield in crop species. Here, we reported a tomato T-DNA mutant, pollen deficient1 (pod1), characterized by an abnormal anther development and the lack of viable pollen formation, which led to the production of parthenocarpic fruits. Genomic analyses and the characterization of silencing lines proved that pod1 mutant phenotype relies on the tomato SlMED18 gene encoding the subunit 18 of Mediator multi-protein complex involved in RNA polymerase II transcription machinery. The loss of SlMED18 function delayed tapetum degeneration, which resulted in deficient microspore development and scarce production of viable pollen. A detailed histological characterization of anther development proved that changes during microgametogenesis and a significant delay in tapetum degeneration are associated with a high proportion of degenerated cells and, hence, should be responsible for the low production of functional pollen grains. Expression of pollen marker genes indicated that SlMED18 is essential for the proper transcription of a subset of genes specifically required to pollen formation and fruit development, revealing a key role of SlMED18 in male gametogenesis of tomato. Additionally, SlMED18 is able to rescue developmental abnormalities of the Arabidopsis med18 mutant, indicating that most biological functions have been conserved in both species.

The drought-tolerant Solanum pennellii regulates leaf water loss and induces genes involved in amino acid and ethylene/jasmonate metabolism under dehydration

Breeding for drought-tolerant crops is a pressing issue due to the increasing frequency and duration of droughts caused by climate change. Although important sources of variation for drought tolerance exist in wild relatives, the mechanisms and the key genes controlling tolerance in tomato are little known. The aim of this study is to determine the drought response of the tomato wild relative Solanum pennellii (Sp) compared with the cultivated tomato Solanum lycopersicum (Sl). The paper investigates the physiological and molecular responses in leaves of Sp and Sl plants without stress and moderate drought stress. Significant physiological differences between species were found, with Sp leaves showing greater ability to avoid water loss and oxidative damage. Leaf transcriptomic analysis carried out when leaves did not as yet show visual dehydration symptoms revealed important constitutive expression differences between Sp and Sl species. Genes linked to different physiological and metabolic processes were induced by drought in Sp, especially those involved in N assimilation, GOGAT/GS cycle and GABA-shunt. Up-regulation in Sp of genes linked to JA/ET biosynthesis and signaling pathways was also observed. In sum, genes involved in the amino acid metabolism together with genes linked to ET/JA seem to be key actors in the drought tolerance of the wild tomato species.

The SlCBL10 Calcineurin B-Like Protein Ensures Plant Growth under Salt Stress by Regulating Na+ and Ca2+ Homeostasis

Characterization of a new tomato (Solanum lycopersicum) T-DNA mutant allowed for the isolation of the CALCINEURIN B-LIKE PROTEIN 10 (SlCBL10) gene whose lack of function was responsible for the severe alterations observed in the shoot apex and reproductive organs under salinity conditions. Physiological studies proved that SlCBL10 gene is required to maintain a proper low Na⁺/Ca²⁺ ratio in growing tissues allowing tomato growth under salt stress. Expression analysis of the main responsible genes for Na⁺ compartmentalization (i.e. Na⁺/H⁺ EXCHANGERs, SALT OVERLY SENSITIVE, HIGH-AFFINITY K+ TRANSPORTER 1;2, H⁺-pyrophosphatase AVP1 [SlAVP1] and V-ATPase [SlVHA-A1]) supported a reduced capacity to accumulate Na⁺ in Slcbl10 mutant leaves, which resulted in a lower uploading of Na⁺ from xylem, allowing the toxic ion to reach apex and flowers. Likewise, the tomato CATION EXCHANGER 1 and TWO-PORE CHANNEL 1 (SlTPC1), key genes for Ca²⁺ fluxes to the vacuole, showed abnormal expression in Slcbl10 plants indicating an impaired Ca²⁺ release from vacuole. Additionally, complementation assay revealed that SlCBL10 is a true ortholog of the Arabidopsis (Arabidopsis thaliana) CBL10 gene, supporting that the essential function of CBL10 is conserved in Arabidopsis and tomato. Together, the findings obtained in this study provide new insights into the function of SlCBL10 in salt stress tolerance. Thus, it is proposed that SlCBL10 mediates salt tolerance by regulating Na⁺ and Ca²⁺ fluxes in the vacuole, cooperating with the vacuolar cation channel SlTPC1 and the two vacuolar H⁺-pumps, SlAVP1 and SlVHA-A1, which in turn are revealed as potential targets of SlCBL10.

A collection of enhancer trap insertional mutants for functional genomics in tomato

With the completion of genome sequencing projects, the next challenge is to close the gap between gene annotation and gene functional assignment. Genomic tools to identify gene functions are based on the analysis of phenotypic variations between a wild type and its mutant; hence, mutant collections are a valuable resource. In this sense, T-DNA collections allow for an easy and straightforward identification of the tagged gene, serving as the basis of both forward and reverse genetic strategies. This study reports on the phenotypic and molecular characterization of an enhancer trap T-DNA collection in tomato (Solanum lycopersicum L.), which has been produced by Agrobacterium-mediated transformation using a binary vector bearing a minimal promoter fused to the uidA reporter gene. Two genes have been isolated from different T-DNA mutants, one of these genes codes for a UTP-glucose-1-phosphate uridylyltransferase involved in programmed cell death and leaf development, which means a novel gene function reported in tomato. Together, our results support that enhancer trapping is a powerful tool to identify novel genes and regulatory elements in tomato and that this T-DNA mutant collection represents a highly valuable resource for functional analyses in this fleshy-fruited model species.

Albino T-DNA tomato mutant reveals a key function of 1-deoxy-D-xylulose-5-phosphate synthase (DXS1) in plant development and survival

Photosynthetic activity is indispensable for plant growth and survival and it depends on the synthesis of plastidial isoprenoids as chlorophylls and carotenoids. In the non-mevalonate pathway (MEP), the 1-deoxy-D-xylulose-5-phosphate synthase 1 (DXS1) enzyme has been postulated to catalyze the rate-limiting step in the formation of plastidial isoprenoids. In tomato, the function of DXS1 has only been studied in fruits, and hence its functional relevance during plant development remains unknown. Here we report the characterization of the wls-2297 tomato mutant, whose severe deficiency in chlorophylls and carotenoids promotes an albino phenotype. Additionally, growth of mutant seedlings was arrested without developing vegetative organs, which resulted in premature lethality. Gene cloning and silencing experiments revealed that the phenotype of wls-2297 mutant was caused by 38.6 kb-deletion promoted by a single T-DNA insertion affecting the DXS1 gene. This was corroborated by in vivo and molecular complementation assays, which allowed the rescue of mutant phenotype. Further characterization of tomato plants overexpressing DXS1 and comparative expression analysis indicate that DXS1 may play other important roles besides to that proposed during fruit carotenoid biosynthesis. Taken together, these results demonstrate that DXS1 is essentially required for the development and survival of tomato plants.

The tomato mutant ars1 (altered response to salt stress 1) identifies an R1-type MYB transcription factor involved in stomatal closure under salt acclimation

A screening under salt stress conditions of a T-DNA mutant collection of tomato (Solanum lycopersicum L.) led to the identification of the altered response to salt stress 1 (ars1) mutant, which showed a salt-sensitive phenotype. Genetic analysis of the ars1 mutation revealed that a single T-DNA insertion in the ARS1 gene was responsible of the mutant phenotype. ARS1 coded for an R1-MYB type transcription factor and its expression was induced by salinity in leaves. The mutant reduced fruit yield under salt acclimation while in the absence of stress the disruption of ARS1 did not affect this agronomic trait. The stomatal behaviour of ars1 mutant leaves induced higher Na(+) accumulation via the transpiration stream, as the decreases of stomatal conductance and transpiration rate induced by salt stress were markedly lower in the mutant plants. Moreover, the mutation affected stomatal closure in a response mediated by abscisic acid (ABA). The characterization of tomato transgenic lines silencing and overexpressing ARS1 corroborates the role of the gene in regulating the water loss via transpiration under salinity. Together, our results show that ARS1 tomato gene contributes to reduce transpirational water loss under salt stress. Finally, this gene could be interesting for tomato molecular breeding, because its manipulation could lead to improved stress tolerance without yield penalty under optimal culture conditions.

Use of enhancer trapping to identify pathogen-induced regulatory events spatially restricted to plant-microbe interaction sites

Plant genes differentially expressed during plant-pathogen interactions can be important for host immunity or can contribute to pathogen virulence. Large-scale transcript profiling studies, such as microarray- or mRNA-seq-based analyses, have revealed hundreds of genes that are differentially expressed during plant-pathogen interactions. However, transcriptional responses limited to a small number of cells at infection sites can be difficult to detect using these approaches, as they are under-represented in the whole-tissue datasets typically generated by such methods. This study examines the interactions between Arabidopsis thaliana (Arabidopsis) and the pathogenic oomycete Hyaloperonospora arabidopsidis (Hpa) by enhancer trapping to uncover novel plant genes involved in local infection responses. We screened a β-glucuronidase (GUS) reporter-based enhancer-trap population for expression patterns related to Hpa infection. Several independent lines exhibited GUS expression in leaf mesophyll cells surrounding Hpa structures, indicating a regulatory response to pathogen infection. One of these lines contained a single enhancer-trap insertion in an exon of At1g08800 (MyoB1, Myosin Binding Protein 1) and was subsequently found to exhibit reduced susceptibility to Hpa. Two additional Arabidopsis lines with T-DNA insertions in exons of MyoB1 also exhibited approximately 30% fewer spores than wild-type plants. This study demonstrates that our enhancer-trapping strategy can result in the identification of functionally relevant pathogen-responsive genes. Our results further suggest that MyoB1 either positively contributes to Hpa virulence or negatively affects host immunity against this pathogen.

Characterization of vegetative inflorescence (mc-vin) mutant provides new insight into the role of MACROCALYX in regulating inflorescence development of tomato

Inflorescence development is a key factor of plant productivity, as it determines flower number. Therefore, understanding the mechanisms that regulate inflorescence architecture is critical for reproductive success and crop yield. In this study, a new mutant, vegetative inflorescence (mc-vin), was isolated from the screening of a tomato (Solanum lycopersicum L.) T-DNA mutant collection. The mc-vin mutant developed inflorescences that reverted to vegetative growth after forming two to three flowers, indicating that the mutated gene is essential for the maintenance of inflorescence meristem identity. The T-DNA was inserted into the promoter region of the MACROCALYX (MC) gene; this result together with complementation test and expression analyses proved that mc-vin is a new knock-out allele of MC. Double combinations between mc-vin and jointless (j) and single flower truss (sft) inflorescence mutants showed that MC has pleiotropic effects on the reproductive phase, and that it interacts with SFT and J to control floral transition and inflorescence fate in tomato. In addition, MC expression was mis-regulated in j and sft mutants whereas J and SFT were significantly up-regulated in the mc-vin mutant. Together, these results provide new evidences about MC function as part of the genetic network regulating the development of tomato inflorescence meristem.

The tomato res mutant which accumulates JA in roots in non-stressed conditions restores cell structure alterations under salinity

Jasmonic acid (JA) regulates a wide spectrum of plant biological processes, from plant development to stress defense responses. The role of JA in plant response to salt stress is scarcely known, and even less known is the specific response in root, the main plant organ responsible for ionic uptake and transport to the shoot. Here we report the characterization of the first tomato (Solanum lycopersicum) mutant, named res (restored cell structure by salinity), that accumulates JA in roots prior to exposure to stress. The res tomato mutant presented remarkable growth inhibition and displayed important morphological alterations and cellular disorganization in roots and leaves under control conditions, while these alterations disappeared when the res mutant plants were grown under salt stress. Reciprocal grafting between res and wild type (WT) (tomato cv. Moneymaker) indicated that the main organ responsible for the development of alterations was the root. The JA-signaling pathway is activated in res roots prior to stress, with transcripts levels being even higher in control condition than in salinity. Future studies on this mutant will provide significant advances in the knowledge of JA role in root in salt-stress tolerance response, as well as in the energy trade-off between plant growth and response to stress.

Guidelines to use tomato in experiments with a controlled environment

Domesticated tomato (Solanum lycopersicum) is the most important horticultural crop worldwide. Low polymorphism at the DNA level conflicts with the wealth of morphological variation. Fruits vary widely in size, shape, and color. In contrast, genetic variation between the 16 wild relatives is tremendous. Several large seed banks provide tomato germplasm for both domesticated and wild accessions of tomato. Recently, the genomes of the inbred cultivar "Heinz 1706" (≈900 Mb), and S. pimpinellifolium (739 Mb) were sequenced. Genomic markers and genome re-sequencing data are available for >150 cultivars and accessions. Transformation of tomato is relatively easy and T-DNA insertion line collections are available. Tomato is widely used as a model crop for fruit development but also for diverse physiological, cellular, biochemical, molecular, and genetic studies. It can be easily grown in greenhouses or growth chambers. Plants grow, flower, and develop fruits well at daily light lengths between 8 and 16 h. The required daily light integral of an experiment depends on growth stage and temperature investigated. Temperature must be 10-35°C, relative humidity 30-90%, and, CO2 concentration 200-1500 μmol mol(-1). Temperature determines the speed of the phenological development while daily light integral and CO2 concentration affect photosynthesis and biomass production. Seed to seed cultivation takes 100 days at 20°C and can be shortened or delayed by temperature. Tomato may be cultivated in soil, substrates, or aeroponically without any substrate. Root volume, and water uptake requirements are primarily determined by transpiration demands of the plants. Many nutrient supply recipes and strategies are available to ensure sufficient supply as well as specific nutrient deficits/surplus. Using appropriate cultivation techniques makes tomato a convenient model plant for researchers, even for beginners.

Microgenomics: genome-scale, cell-specific monitoring of multiple gene regulation tiers

The expression of nuclear protein-coding genes is controlled by dynamic mechanisms ranging from DNA methylation, chromatin modification, and gene transcription to mRNA maturation, turnover, and translation and the posttranslational control of protein function. A genome-scale assessment of the spatiotemporal regulation of gene expression is essential for a comprehensive understanding of gene regulatory networks. However, there are major obstacles to the precise evaluation of gene regulation in multicellular plant organs; these include the monitoring of regulatory processes at levels other than steady-state transcript abundance, resolution of gene regulation in individual cells or cell types, and effective assessment of transient gene activity manifested during development or in response to external cues. This review surveys the advantages and applications of microgenomics technologies that enable panoramic quantitation of cell-type-specific expression in plants, focusing on the importance of querying gene activity at multiple steps in the continuum, from histone modification to selective translation.

Production of engineered long-life and male sterile Pelargonium plants

BACKGROUND

Pelargonium is one of the most popular garden plants in the world. Moreover, it has a considerable economic importance in the ornamental plant market. Conventional cross-breeding strategies have generated a range of cultivars with excellent traits. However, gene transfer via Agrobacterium tumefaciens could be a helpful tool to further improve Pelargonium by enabling the introduction of new genes/traits. We report a simple and reliable protocol for the genetic transformation of Pelargonium spp. and the production of engineered long-life and male sterile Pelargonium zonale plants, using the pSAG12::ipt and PsEND1::barnase chimaeric genes respectively.

RESULTS

The pSAG12::ipt transgenic plants showed delayed leaf senescence, increased branching and reduced internodal length, as compared to control plants. Leaves and flowers of the pSAG12::ipt plants were reduced in size and displayed a more intense coloration. In the transgenic lines carrying the PsEND1::barnase construct no pollen grains were observed in the modified anther structures, which developed instead of normal anthers. The locules of sterile anthers collapsed 3-4 days prior to floral anthesis and, in most cases, the undeveloped anther tissues underwent necrosis.

CONCLUSION

The chimaeric construct pSAG12::ipt can be useful in Pelargonium spp. to delay the senescence process and to modify plant architecture. In addition, the use of engineered male sterile plants would be especially useful to produce environmentally friendly transgenic plants carrying new traits by preventing gene flow between the genetically modified ornamentals and related plant species. These characteristics could be of interest, from a commercial point of view, both for pelargonium producers and consumers.

Overexpression of dehydrin tas14 gene improves the osmotic stress imposed by drought and salinity in tomato

One strategy to increase the level of drought and salinity tolerance is the transfer of genes codifying different types of proteins functionally related to macromolecules protection, such as group 2 of late embryogenesis abundant (LEA) proteins or dehydrins. The TAS14 dehydrin was isolated and characterized in tomato and its expression was induced by osmotic stress (NaCl and mannitol) and abscisic acid (ABA) [Godoy et al., Plant Mol Biol 1994;26:1921-1934], yet its function in drought and salinity tolerance of tomato remains elusive. In this study, transgenic tomato plants overexpressing tas14 gene under the control of the 35SCaMV promoter were generated to assess the function of tas14 gene in drought and salinity tolerance. The plants overexpressing tas14 gene achieved improved long-term drought and salinity tolerance without affecting plant growth under non-stress conditions. A mechanism of osmotic stress tolerance via osmotic potential reduction and solutes accumulation, such as sugars and K(+) is operating in tas14 overexpressing plants in drought conditions. A similar mechanism of osmotic stress tolerance was observed under salinity. Moreover, the overexpression of tas14 gene increased Na(+) accumulation only in adult leaves, whereas in young leaves, the accumulated solutes were K(+) and sugars, suggesting that plants overexpressing tas14 gene are able to distribute the Na(+) accumulation between young and adult leaves over a prolonged period in stressful conditions. Measurement of ABA showed that the action mechanism of tas14 gene is associated with an earlier and greater accumulation of ABA in leaves during short-term periods. A good feature for the application of this gene in improving drought and salt stress tolerance is the fact that its constitutive expression does not affect plant growth under non-stress conditions, and tolerance induced by overexpression of tas14 gene was observed at the different stress degrees applied to the long term.