Characterization of a shoot-specific, GA3- and ABA-regulated gene from tomato

Identification and Functional Exploration of BraGASA Genes Reveal Their Potential Roles in Drought Stress Tolerance and Sexual Reproduction in Brassica rapa L. ssp. pekinensis

Gibberellic acid-stimulated Arabidopsis sequences (GASAs) are a subset of the gibberellin (GA)-regulated gene family and play crucial roles in various physiological processes. However, the GASA genes in Brassica rapa have not yet been documented. In this study, we identified and characterized 16 GASA genes in Chinese cabbage (Brassica rapa L. ssp. pekinensis). Analysis of the conserved motifs revealed significant conservation within the activation segment of BraGASA genes. This gene family contains numerous promoter elements associated with abiotic stress tolerance, including those for abscisic acid (ABA) and methyl jasmonate (MeJA). Expression profiling revealed the presence of these genes in various tissues, including roots, stems, leaves, flowers, siliques, and callus tissues. When plants were exposed to drought stress, the expression of BraGASA3 decreased notably in drought-sensitive genotypes compared to their wild-type counterparts, highlighting the potentially crucial role of BraGASA3 in drought stress. Additionally, BraGASAs exhibited various functions in sexual reproduction dynamics. The findings contribute to the understanding of the function of BraGASAs and provide valuable insights for further exploration of the GASA gene function of the BraGASA gene in Chinese cabbage.

Genome-Wide Identification and Characterization of the GASA Gene Family in Medicago truncatula, and Expression Patterns under Abiotic Stress and Hormone Treatments

Medicago truncatula is a key model plant for studying legume plants, particularly alfalfa (Medicago sativa), due to its well-defined genetic background. Plant-specific GASA (Gibberellic Acid Stimulated Arabidopsis) genes play various roles in plant growth and development, abiotic stress, and hormone responses. However, limited information is available on GASA research in Medicago. In this study, 26 MtGASAs were identified and analyzed for its structure, evolution, and expressions. Sequence alignments and phylogeny revealed that 26 MtGASAs containing conserved GASA domains were classified into three clades. The chromosomal locations and gene synteny revealed segmental and tandem repetition evolution. Analysis of cis-regulatory elements indicates that family members likely influence various hormone signaling pathways and stress-related mechanisms. Moreover, the RNA-seq and qRT-PCR analyses revealed that 26 MtGASAs were extensively involved in abiotic stresses and hormone responses. Notably, seven MtGASA genes (MtGASA1, 10, 12, 17, 23, 25 and 26) were all dramatically activated by NaCl and Mannitol treatments, and four MtGASAs (MtGASA7, 10, 23 and 24) were significant activated by GA3, PBZ, ABA, and MeJA treatments. Collectively, this study is the first to identify and describe GASA genes in Medicago on a genome-wide scale. The results establish a basis for functional characterization, showing that these proteins are essential in responding to various abiotic stresses and hormonal signals.

Development of a marker-free engineered durum wheat overexpressing Lobularia maritima GASA1 with improved drought tolerance

Due to their fixed lifestyle, plants must adapt to abiotic or biotic stresses by orchestrating various responses, including protective and growth control measures. Growth arrest is provoked upon abiotic stress and can impair plant production. Members of the plant-specific GASA (gibberellic acid-stimulated Arabidopsis) gene family play crucial roles in phytohormone responses, abiotic and biotic stresses, and plant growth. Here, we recognized and examined the LmGASA1 gene from the halophyte plant Lobularia maritima and developed marker-free engineered durum wheat plants overexpressing the gene. The LmGASA1 transcript profile revealed that it's induced by stressful events as well as by phytohormones including GA3, MeJA, and ABA, suggesting that the LmGASA1 gene may contribute to these stress and hormone signal transduction pathways. Transient expression of GFP-LmGASA1 fusion in onion epidermal cells indicated that LmGASA1 is localized to the cell membrane. Further analysis showed that overexpression of LmGASA1 in durum wheat plants enhanced tolerance to drought stress compared with that in non-transgenic (NT) plants, imposing no yield penalty and enabling seed production even following drought stress at the vegetative stage. Altogether, our data indicate that LmGASA1 regulates both the scavenging capacity of the antioxidant enzymatic system and the activation of at least six stress-related genes that function as positive regulators of drought stress tolerance. LmGASA1 appears to be a novel gene useful for further functional analysis and potential engineering for drought stress tolerance in crops.

The Stylo Cysteine-Rich Peptide SgSnakin1 Is Involved in Aluminum Tolerance through Enhancing Reactive Oxygen Species Scavenging

Stylo (Stylosanthes spp.) is an important pasture legume with strong aluminum (Al) resistance. However, the molecular mechanisms underlying its Al tolerance remain fragmentary. Due to the incomplete genome sequence information of stylo, we first conducted full-length transcriptome sequencing for stylo root tips treated with and without Al and identified three Snakin/GASA genes, namely, SgSnakin1, SgSnakin2, and SgSnakin3. Through quantitative RT-PCR, we found that only SgSnakin1 was significantly upregulated by Al treatments in stylo root tips. Histochemical localization assays further verified the Al-enhanced expression of SgSnakin1 in stylo root tips. Subcellular localization in both tobacco and onion epidermis cells showed that SgSnakin1 localized to the cell wall. Overexpression of SgSnakin1 conferred Al tolerance in transgenic Arabidopsis, as reflected by higher relative root growth and cell vitality, as well as lower Al concentration in the roots of transgenic plants. Additionally, overexpression of SgSnakin1 increased the activities of SOD and POD and decreased the levels of O2·- and H2O2 in transgenic Arabidopsis in response to Al stress. These findings indicate that SgSnakin1 may function in Al resistance by enhancing the scavenging of reactive oxygen species through the regulation of antioxidant enzyme activities.

GhGASA14 regulates the flowering time of upland cotton in response to GA3

KEY MESSAGE

The silencing of GhGASA14 and the identification of superior allelic variation in its coding region indicate that GhGASA14 may positively regulate flowering and the response to GA3. Gibberellic acid-stimulated Arabidopsis (GASA), a member of the gibberellin-regulated short amino acid family, has been extensively investigated in several plant species and found to be critical for plant growth and development. However, research on this topic in cotton has been limited. In this study, we identified 38 GhGASAs that were dispersed across 18 chromosomes in upland cotton, and all of these genes had a GASA core domain. Transcriptome expression patterns and qRT-PCR results revealed that GhGASA9 and GhGASA14 exhibited upregulated expression not only in the floral organs but also in the leaves of early-maturing cultivars. The two genes were functionally characterized by virus-induced gene silencing (VIGS), and the budding and flowering times after silencing the target genes were later than those of the control (TRV:00). Compared with that in the water-treated group (MOCK), the flowering period of the different fruiting branches in the GA3-treated group was more concentrated. Interestingly, allelic variation was detected in the coding sequence of GhGASA14 between early-maturing and late-maturing accessions, and the frequency of this favorable allele was greater in high-latitude cotton cultivars than in low-latitude ones. Additionally, a significant linear relationship was observed between the expression level of GhGASA14 and flowering time among the 12 upland cotton accessions. Taken together, these results indicated that GhGASA14 may positively regulate flowering time and respond to GA3. These findings could lead to the use of valuable genetic resources for breeding early-maturing cotton cultivars in the future.

Unveiling the defensive role of Snakin-3, a member of the subfamily III of Snakin/GASA peptides in potatoes

KEY MESSAGE

The first in-depth characterization of a subfamily III Snakin/GASA member was performed providing experimental evidence on promoter activity and subcellular localization and unveiling a role of potato Snakin-3 in defense Snakin/GASA proteins share 12 cysteines in conserved positions in the C-terminal region. Most of them were involved in different aspects of plant growth and development, while a small number of these peptides were reported to have antimicrobial activity or participate in abiotic stress tolerance. In potato, 18 Snakin/GASA genes were identified and classified into three groups based on phylogenetic analysis. Snakin-1 and Snakin-2 are members of subfamilies I and II, respectively, and were reported to be implicated not only in defense against pathogens but also in plant development. In this work, we present the first in-depth characterization of Snakin-3, a member of the subfamily III within the Snakin/GASA gene family of potato. Transient co-expression of Snakin-3 fused to the green fluorescent protein and organelle markers revealed that it is located in the endoplasmic reticulum. Furthermore, expression analyses via pSnakin-3::GUS transgenic plants showed GUS staining mainly in roots and vascular tissues of the stem. Moreover, GUS expression levels were increased after inoculation with Pseudomonas syringae pv. tabaci or Pectobacterium carotovorum subsp. carotovorum and also after auxin treatment mainly in roots and stems. To gain further insights into the function of Snakin-3 in planta, potato overexpressing lines were challenged against P. carotovorum subsp. carotovorum showing enhanced tolerance to this bacterial pathogen. In sum, here we report the first functional characterization of a Snakin/GASA gene from subfamily III in Solanaceae. Our findings provide experimental evidence on promoter activity and subcellular localization and reveal a role of potato Snakin-3 in plant defense.

Genome-Wide Identification and Comprehensive Analysis of the GASA Gene Family in Peanuts (Arachis hypogaea L.) under Abiotic Stress

Peanut (Arachis hypogaea L.) is a globally cultivated crop of significant economic and nutritional importance. The role of gibberellic-acid-stimulated Arabidopsis (GASA) family genes is well established in plant growth, development, and biotic and abiotic stress responses. However, there is a gap in understanding the function of GASA proteins in cultivated peanuts, particularly in response to abiotic stresses such as drought and salinity. Thus, we conducted comprehensive in silico analyses to identify and verify the existence of 40 GASA genes (termed AhGASA) in cultivated peanuts. Subsequently, we conducted biological experiments and performed expression analyses of selected AhGASA genes to elucidate their potential regulatory roles in response to drought and salinity. Phylogenetic analysis revealed that AhGASA genes could be categorized into four distinct subfamilies. Under normal growth conditions, selected AhGASA genes exhibited varying expressions in young peanut seedling leaves, stems, and roots tissues. Notably, our findings indicate that certain AhGASA genes were downregulated under drought stress but upregulated under salt stress. These results suggest that specific AhGASA genes are involved in the regulation of salt or drought stress. Further functional characterization of the upregulated genes under both drought and salt stress will be essential to confirm their regulatory roles in this context. Overall, our findings provide compelling evidence of the involvement of AhGASA genes in the mechanisms of stress tolerance in cultivated peanuts. This study enhances our understanding of the functions of AhGASA genes in response to abiotic stress and lays the groundwork for future investigations into the molecular characterization of AhGASA genes.

Genome-Wide Identification and Characterization of Gibberellic Acid-Stimulated Arabidopsis Gene Family in Pineapple (Ananas comosus)

The gibberellic acid-stimulated Arabidopsis (GASA) gene family plays a crucial role in growth, development, and stress response, and it is specific to plants. This gene family has been extensively studied in various plant species, and its functional role in pineapple has yet to be characterized. In this study, 15 AcGASA genes were identified in pineapple through a genome-wide scan and categorized into three major branches based on a phylogenetic tree. All AcGASA proteins share a common structural domain with 12 cysteine residues, but they exhibit slight variations in their physicochemical properties and motif composition. Predictions regarding subcellular localization suggest that AcGASA proteins are present in the cell membrane, Golgi apparatus, nucleus, and cell wall. An analysis of gene synteny indicated that both tandem and segmental repeats have a significant impact on the expansion of the AcGASA gene family. Our findings demonstrate the differing regulatory effects of these hormones (GA, NAA, IAA, MeJA, and ABA) on the AcGASA genes. We analyzed the expression profiles of GASA genes in different pineapple tissue parts, and the results indicated that AcGASA genes exhibit diverse expression patterns during the development of different plant tissues, particularly in the regulation of floral organ development. This study provides a comprehensive understanding of GASA family genes in pineapple. It serves as a valuable reference for future studies on the functional characterization of GASA genes in other perennial herbaceous plants.

Overexpression of SlPRE3 alters the plant morphologies in Solanum lycopersicum

KEY MESSAGE

Overexpression of SlPRE3 is detrimental to the photosynthesis and alters plant morphology and root development. SlPRE3 interacts with SlAIF1/SlAIF2/SlPAR1/SlIBH1 to regulate cell expansion. Basic helix-loop-helix (bHLH) transcription factors play crucial roles as regulators in plant growth and development. In this study, we isolated and characterized SlPRE3, an atypical bHLH transcription factor gene. SlPRE3 exhibited predominant expression in the root and moderate expression in the senescent leaves. Comparative analysis with the wild type revealed significant differences in plant morphology in the 35S:SlPRE3 lines. These differences included increased internode length, rolling leaves with reduced chlorophyll accumulation, and elongated yet fewer adventitious roots. Additionally, 35S:SlPRE3 lines displayed elevated levels of GA3 (gibberellin A3) and reduced starch accumulation. Furthermore, utilizing the Y2H (Yeast two-hybrid) and the BiFC (Bimolecular Fluorescent Complimentary) techniques, we identified physical interactions between SlPRE3 and SlAIF1 (ATBS1-interacting factor 1)/SlAIF2 (ATBS1-interacting factor 2)/SlPAR1 (PHYTOCHROME RAPIDLY REGULATED 1)/SlIBH1 (ILI1-binding bHLH 1). RNA-seq analysis of root tissues revealed significant alterations in transcript levels of genes involved in gibberellin metabolism and signal transduction, cell expansion, and root development. In summary, our study sheds light on the crucial regulatory role of SlPRE3 in determining plant morphology and root development.

Transcriptome and metabolome analyses of Shatian pomelo (Citrus grandis var. Shatinyu Hort) leaves provide insights into the overexpression of the gibberellin-induced gene CcGASA4

The gibberellic acid (GA)-stimulated Arabidopsis (GASA) gene family is highly specific to plants and plays crucial roles in plant growth and development. CcGASA4 is a member of the GASA gene family in citrus plants; however, the current understanding of its function in citrus is limited. We used CcGASA4-overexpression transgenic citrus (OEGA) and control (CON) plants to study the role of CcGASA4 in Shatian pomelo. The RNA sequencing (RNA-seq) analysis showed that 3,522 genes, including 1,578 upregulated and 1,944 downregulated genes, were significantly differentially expressed in the CON versus OEGA groups. The Gene Ontology enrichment analysis showed that 178 of the differentially-expressed genes (DEGs) were associated with flowers. A Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the DEGs were enriched in 134 pathways, including "plant-pathogen interaction", "MAPK signaling pathway-plant", "phenylpropane biosynthesis", "plant hormone signal transduction", "phenylalanine, tyrosine and tryptophan biosynthesis", and "flavonoid and flavonol biosynthesis". The most significantly-enriched pathway was "plant-pathogen interaction", in which 203 DEGs were enriched (126 DEGs were upregulated and 78 were downregulated). The metabolome analysis showed that 644 metabolites were detected in the OEGA and CON samples, including 294 differentially-accumulated metabolites (DAMs; 83 upregulated versus 211 downregulated in OEGA compared to CON). The metabolic pathway analysis showed that these DAMs were mainly involved in the metabolic pathways of secondary metabolites, such as phenylpropanoids, phenylalanine, flavone, and flavonol biosynthesis. Thirteen flavonoids and isoflavones were identified as DAMs in OEGA and CON. We also discovered 25 OEGA-specific accumulated metabolites and found 10 that were associated with disease resistance. CcGASA4 may therefore play a functional role in activating the expression of MAPK signaling transduction pathway and disease resistance genes, inhibiting the expression of auxin- and ethylene-related genes, and activating or inhibiting the expression of brassinosteroid biosynthesis- and abscisic acid-related genes. CcGASA4 may also play a role in regulating the composition and abundance of flavonoids, isoflavones, amino acids, purines, and phenolic compounds. This study provides new insights into the molecular mechanisms of action of CcGASA4 in citrus plants.

ABA and Bud Dormancy in Perennials: Current Knowledge and Future Perspective

Bud dormancy is an evolved trait that confers adaptation to harsh environments, and affects flower differentiation, crop yield and vegetative growth in perennials. ABA is a stress hormone and a major regulator of dormancy. Although the physiology of bud dormancy is complex, several advancements have been achieved in this field recently by using genetics, omics and bioinformatics methods. Here, we review the current knowledge on the role of ABA and environmental signals, as well as the interplay of other hormones and sucrose, in the regulation of this process. We also discuss emerging potential mechanisms in this physiological process, including epigenetic regulation.

The GASA Gene Family in Theobroma cacao: Genome wide Identification and Expression Analysis.. [DOI: 10.1101/2021.01.27.425041]

The gibberellic acid-stimulated Arabidopsis (GASA/GAST) gene family is widely distributed in plants. The role of the GASA gene family has been reported previously in various physiological and biological processes, such as cell division, root and seed development, stem growth, and fruit ripening. These genes also provide resistance to abiotic and biotic stresses including antimicrobial, antiviral, and antifungal. Here, we report 17 tcGASA genes in Theobroma cacao L. distributed on six chromosomes. The gene structure, promoter-region sequences, protein structure, and biochemical properties, expression, and phylogenetics of all tcGASAs were analyzed. Phylogenetic analyses divided tcGASA proteins into five groups. The nine segmentally duplicating genes form four pairs and cluster together in phylogenetic tree. Purifying selection pressure was recorded on tcGASA, including duplicated genes. Several stress/hormone-responsive cis-regulatory elements were also recognized in the promoter region of tcGASAs. Differential expression analyses revealed that most of the tcGASA genes showed elevated expression in the seeds (cacao food), implying their role in seed development. The black rod disease of genus Phytophthora caused up to 20–25% loss (700,000 metric tons) in world cacao production. The role of tcGASA genes in conferring fungal resistance was also explored based on RNAseq data against Phytophthora megakarya. The differential expression of tcGASA genes was recorded between the tolerant and susceptible cultivars of cacao plants, which were inoculated with the fungus for 24h and 72h. This differential expression indicating possible role of tcGASA genes to fungal resistant in cacao. Our findings provide new insight into the function, evolution, and regulatory system of the GASA family genes in T. cacao and provide new target genes for development of fungi-resistant cacao varieties in breeding programs.

A quantitative trait locus GW6 controls rice grain size and yield through the gibberellin pathway

Grain size is one of the essential components determining rice yield and is a target for both domestication and artificial breeding. Gibberellins (GAs) are diterpenoid phytohormones that influence diverse aspects of plant growth and development. Several quantitative trait loci (QTLs) have been identified that control grain size through phytohormone regulation. However, little is known about the role of GAs in the control of grain size. Here we report the cloning and characterization of a QTL, GW6 (GRAIN WIDTH 6), which encodes a GA-regulated GAST family protein and positively regulates grain width and weight. GW6 is highly expressed in the young panicle and increases grain width by promoting cell expansion in the spikelet hull. Knockout of GW6 exhibits reduced grain size and weight, whereas overexpression of GW6 results in increased grain size and weight. GW6 is induced by GA and its knockout downregulates the expression of GA biosynthesis genes and decreases GA content in the young panicle. We found that a natural variation in the cis element CAAT-box in the promoter of GW6 is associated with its expression level and grain width and weight. Furthermore, introduction of GW6 to Oryza indica variety HJX74 can lead to a 10.44% increase in rice grain yield, indicating that GW6 has great potential to improve grain yield in rice.

A New Insight into Flowering Regulation: Molecular Basis of Flowering Initiation in Magnolia × soulangeana 'Changchun'

Magnolia × soulangeana ‘Changchun’ are trees that bloom in spring and summer respectively after flower bud differentiation. Here, we use phenological and morphological observation and RNA-seq technology to study the molecular basis of flowering initiation in ‘Changchun’. During the process of flowering initiation in spring and summer, the growth of expanded flower buds increased significantly, and their shape was obviously enlarged, which indicated that flowering was initiated. A total of 168,120 expressed genes were identified in spring and summer dormant and expanded flower buds, of which 11,687 genes showed significantly differential expression between spring and summer dormant and expanded flower buds. These differentially expressed genes (DEGs) were mainly involved in plant hormone signal transduction, metabolic processes, cellular components, binding, and catalytic activity. Analysis of differential gene expression patterns revealed that gibberellin signaling, and some transcription factors were closely involved in the regulation of spring and summer flowering initiation in ‘Changchun’. A qRT-PCR (quantitative Real Time Polymerase Chain Reaction) analysis showed that BGISEQ-500 sequencing platform could truly reflect gene expression patterns. It also verified that GID1B (GIBBERELLIN INSENSITIVE DWARF1 B), GID1C, SPL8 (SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 8), and GASA (GIBBERELLIC ACID-STIMULATED ARABIDOPSIS) family genes were expressed at high levels, while the expression of SPY (SPINDLY) was low during spring and summer flowering initiation. Meanwhile, the up- and down-regulated expression of, respectively, AGL6 (AGAMOUS-LIKE 6) and DREB3 (DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEIN 3), AG15, and CDF1 (CYCLIC DOF FACTOR 1) might also be involved in the specific regulation of spring and summer flowering initiation. Obviously, flowering initiation is an important stage of the flowering process in woody plants, involving the specific regulation of relevant genes and transcription factors. This study provides a new perspective for the regulation of the flowering process in perennial woody plants.

Identification and Analysis of the GASR Gene Family in Common Wheat (Triticum aestivum L.) and Characterization of TaGASR34, a Gene Associated With Seed Dormancy and Germination

Seed dormancy and germination are important agronomic traits in wheat (Triticum aestivum L.) because they determine pre-harvest sprouting (PHS) resistance and thus affect grain production. These processes are regulated by Gibberellic Acid-Stimulated Regulator (GASR) genes. In this study, we identified 37 GASR genes in common wheat, which were designated TaGASR1-37. Moreover, we identified 40 pairs of paralogous genes, of which only one had a Ka/Ks value greater than 1, indicating that most TaGASR genes have undergone negative selection. Chromosomal location and duplication analysis revealed 25 pairs of segmentally duplicated genes and seven pairs of tandemly duplicated genes, suggesting that large-scale duplication events may have contributed to the expansion of TaGASR gene family. Microarray analysis of the expression of 18 TaGASR genes indicated that these genes play diverse roles in different biological processes. Using wheat varieties with contrasting seed dormancy phenotypes, we investigated the expression patterns of TaGASR genes and the corresponding seed germination index phenotypes in response to water imbibition, exogenous ABA and GA treatment, and low- and high-temperature treatment. Based on these data, we identified the TaGASR34 gene as potentially associated with seed dormancy and germination. Further, we used a SNP mutation of the TaGASR34 promoter (-16) to develop the CAPS marker GS34-7B, which was then used to validate the association of TaGASR34 with seed dormancy and germination by evaluating two natural populations across environments. Notably, the frequency of the high-dormancy GS34-7Bb allele was significantly lower than that of the low-dormancy GS34-7Ba allele, implying that the favorable GS34-7Bb allele has not previously been used in wheat breeding. These results provide valuable information for further functional analysis of TaGASR genes and present a useful gene and marker combination for future improvement of PHS resistance in wheat.

Over-expression of GmSN1 enhances virus resistance in Arabidopsis and soybean

KEY MESSAGE

GmSN1 enhances virus resistance in plants most likely by affecting the expression of signal transduction and immune response genes. Soybean mosaic virus (SMV) infection causes severe symptom and leads to massive yield loss in soybean (Glycine max). By comparative analyzing gene expression in the SMV-resistant soybean cultivar Rsmv1 and the susceptible cultivar Ssmv1 at a transcriptome level, we found that a subgroup of Gibberellic Acid Stimulated Transcript (GAST) genes were down-regulated in SMV inoculated Ssmv1 plants, but not Rsmv1 plants. Sequence alignment and phylogenetic analysis indicated that one of the GAST genes, GmSN1, was closely related to Snakin-1, a well-characterized potato microbial disease resistance gene. When over-expressed in Arabidopsis and soybean, respectively, under the control of the 35S promoter, GmSN1 enhanced turnip mosaic virus resistance in the transgenic Arabidopsis plants, and SMV resistance in the transgenic soybean plants, respectively. Transcriptome analysis results showed that the up-regulated genes in the 35S:GmSN1 transgenic Arabidopsis plants were largely enriched in functional terms including "signal transduction" and "immune response". Real-time PCR assay indicated that the expression of GmAKT2, a potassium channel gene known to enhance SMV resistance when over-expressed in soybean, was elevated in the 35S:GmSN1 transgenic soybean plants. Taken together, our results suggest that GmSN1 enhances virus resistance in plants most likely by affecting the expression of signal transduction and immune response genes.

One new kind of phytohormonal signaling integrator: Up-and-coming GASA family genes

GASA proteins are characterized by an N-terminal signal peptide and a C-terminal conserved GASA domain with 12 invariant cysteine residues. Despite being widely distributed among plant species, their functions are not completely elucidated and little is known about their mechanism of action. This review focuses on the current knowledge about the molecular structure, protein subcellular localization and phytohormones responses of this up-and-coming family of peptides. Furthermore, we discussed the roles of GASA proteins in plant growth and development, plant responses to biotic or abiotic stresses and their participation in phytohormonal signaling integration.

A Mini Zinc-Finger Protein (MIF) from Gerbera hybrida Activates the GASA Protein Family Gene, GEG, to Inhibit Ray Petal Elongation

Petal appearance is an important horticultural trail that is generally used to evaluate the ornamental value of plants. However, knowledge of the molecular regulation of petal growth is mostly derived from analyses of Arabidopsis thaliana, and relatively little is known about this process in ornamental plants. Previously, GEG (Gerbera hybrida homolog of the gibberellin [GA]-stimulated transcript 1 [GAST1] from tomato), a gene from the GA stimulated Arabidopsis (GASA) family, was reported to be an inhibitor of ray petal growth in the ornamental species, G. hybrida. To explore the molecular regulatory mechanism of GEG in petal growth inhibition, a mini zinc-finger protein (MIF) was identified using yeast one-hybrid (Y1H) screen. The direct binding of GhMIF to the GEG promoter was verified by using an electrophoretic mobility shift assay and a dual-luciferase assay. A yeast two-hybrid (Y2H) revealed that GhMIF acts as a transcriptional activator. Transient transformation assay indicated that GhMIF is involved in inhibiting ray petal elongation by activating the expression of GEG. Spatiotemporal expression analyses and hormone treatment assay showed that the expression of GhMIF and GEG is coordinated during petal development. Taken together, these results suggest that GhMIF acts as a direct transcriptional activator of GEG, a gene from the GASA protein family to regulate the petal elongation.

Overexpression of snakin-1 gene enhances resistance to Rhizoctonia solani and Erwinia carotovora in transgenic potato plants

Snakin-1 (SN1), a cysteine-rich peptide with broad-spectrum antimicrobial activity in vitro, was evaluated for its ability to confer resistance to pathogens in transgenic potatoes. Genetic variants of this gene were cloned from wild and cultivated Solanum species. Nucleotide sequences revealed highly evolutionary conservation with 91-98% identity values. Potato plants (S. tuberosum subsp. tuberosum cv. Kennebec) were transformed via Agrobacterium tumefaciens with a construct encoding the S. chacoense SN1 gene under the regulation of the ubiquitous CaMV 35S promoter. Transgenic lines were molecularly characterized and challenged with either Rhizoctonia solani or Erwinia carotovora to analyse whether constitutive in vivo overexpression of the SN1 gene may lead to disease resistance. Only transgenic lines that accumulated high levels of SN1 mRNA exhibited significant symptom reductions of R. solani infection such as stem cankers and damping-off. Furthermore, these overexpressing lines showed significantly higher survival rates throughout the fungal resistance bioassays. In addition, the same lines showed significant protection against E. carotovora measured as: a reduction of lesion areas (from 46.5 to 88.1% with respect to the wild-type), number of fallen leaves and thickened or necrotic stems. Enhanced resistance to these two important potato pathogens suggests in vivo antifungal and antibacterial activity of SN1 and thus its possible biotechnological application.