A molecular marker for lateral root initiation: the RSI-1 gene of tomato (Lycopersicon esculentum Mill) is activated in early lateral root primordia

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.

Cultivating potential: Harnessing plant stem cells for agricultural crop improvement

Meristems are stem cell-containing structures that produce all plant organs and are therefore important targets for crop improvement. Developmental regulators control the balance and rate of cell divisions within the meristem. Altering these regulators impacts meristem architecture and, as a consequence, plant form. In this review, we discuss genes involved in regulating the shoot apical meristem, inflorescence meristem, axillary meristem, root apical meristem, and vascular cambium in plants. We highlight several examples showing how crop breeders have manipulated developmental regulators to modify meristem growth and alter crop traits such as inflorescence size and branching patterns. Plant transformation techniques are another innovation related to plant meristem research because they make crop genome engineering possible. We discuss recent advances on plant transformation made possible by studying genes controlling meristem development. Finally, we conclude with discussions about how meristem research can contribute to crop improvement in the coming decades.

Genome-wide identification and expression analysis of the GASA gene family in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

BACKGROUND

The Gibberellic Acid-Stimulated Arabidopsis (GASA) gene family is widely involved in the regulation of plant growth, development, and stress response. However, information on the GASA gene family has not been reported in Chinese cabbage (Brassica rapa L. ssp. pekinensis).

RESULTS

Here, we conducted genome-wide identification and analysis of the GASA genes in Chinese cabbage. In total, 15 GASA genes were identified in the Chinese cabbage genome, and the physicochemical property, subcellular location, and tertiary structure of the corresponding GASA proteins were elucidated. Phylogenetic analysis, conserved motif, and gene structure showed that the GASA proteins were divided into three well-conserved subfamilies. Synteny analysis proposed that the expansion of the GASA genes was influenced mainly by whole-genome duplication (WGD) and transposed duplication (TRD) and that duplication gene pairs were under negative selection. Cis-acting elements of the GASA promoters were involved in plant development, hormonal and stress responses. Expression profile analysis showed that the GASA genes were widely expressed in different tissues of Chinese cabbage, but their expression patterns appeared to diverse. The qRT-PCR analysis of nine GASA genes confirmed that they responded to salt stress, heat stress, and hormonal triggers.

CONCLUSIONS

Overall, this study provides a theoretical basis for further exploring the important role of the GASA gene family in the functional genome of Chinese cabbage.

Multiple gene co-options underlie the rapid evolution of sexually deceptive flowers in Gorteria diffusa

Gene co-option, the redeployment of an existing gene in an unrelated developmental context, is an important mechanism underlying the evolution of morphological novelty. In most cases described to date, novel traits emerged by co-option of a single gene or genetic network. Here, we show that the integration of multiple co-opted genetic elements facilitated the rapid evolution of complex petal spots that mimic female bee-fly pollinators in the sexually deceptive South African daisy Gorteria diffusa. First, co-option of iron homeostasis genes altered petal spot pigmentation, producing a color similar to that of female pollinators. Second, co-option of the root hair gene GdEXPA7 enabled the formation of enlarged papillate petal epidermal cells, eliciting copulation responses from male flies. Third, co-option of the miR156-GdSPL1 transcription factor module altered petal spot placement, resulting in better mimicry of female flies resting on the flower. The three genetic elements were likely co-opted sequentially, and strength of sexual deception in different G. diffusa floral forms strongly correlates with the presence of the three corresponding morphological alterations. Our findings suggest that gene co-options can combine in a modular fashion, enabling rapid evolution of novel complex traits.

Modifying Anthocyanins Biosynthesis in Tomato Hairy Roots: A Test Bed for Plant Resistance to Ionizing Radiation and Antioxidant Properties in Space

Gene expression manipulation of specific metabolic pathways can be used to obtain bioaccumulation of valuable molecules and desired quality traits in plants. A single-gene approach to impact different traits would be greatly desirable in agrospace applications, where several aspects of plant physiology can be affected, influencing growth. In this work, MicroTom hairy root cultures expressing a MYB-like transcription factor that regulates the biosynthesis of anthocyanins in Petunia hybrida (PhAN4), were considered as a testbed for bio-fortified tomato whole plants aimed at agrospace applications. Ectopic expression of PhAN4 promoted biosynthesis of anthocyanins, allowing to profile 5 major derivatives of delphinidin and petunidin together with pelargonidin and malvidin-based anthocyanins, unusual in tomato. Consistent with PhAN4 features, transcriptomic profiling indicated upregulation of genes correlated to anthocyanin biosynthesis. Interestingly, a transcriptome reprogramming oriented to positive regulation of cell response to biotic, abiotic, and redox stimuli was evidenced. PhAN4 hairy root cultures showed the significant capability to counteract reactive oxygen species (ROS) accumulation and protein misfolding upon high-dose gamma irradiation, which is among the most potent pro-oxidant stress that can be encountered in space. These results may have significance in the engineering of whole tomato plants that can benefit space agriculture.

Genome-Wide Identification and Characterization of GASA Gene Family in Nicotiana tabacum

The gibberellic acid stimulated Arabidopsis (GASA) gene family is critical for plant growth, development, and stress response. GASA gene family has been studied in various plant species, however, the GASA gene family in tobacco (Nicotiana tabacum) have not been characterized in detail. In this study, we identified 18 GASA genes in the tobacco genome, which were distributed to 13 chromosomes. All the proteins contained a conserved GASA domain and highly specific 12-cysteine residues at the C-terminus. Phylogenetic analysis divided the NtGASA genes into three well-conserved subfamilies. Synteny analysis suggested that tandem and segmental duplications played an important role in the expansion of the NtGASA gene family. Cis-elements analysis showed that NtGASA genes might influence different phytohormone and stress responses. Tissue expression analysis revealed that NtGASA genes displayed unique or distinct expression patterns in different tissues, suggesting their potential roles in plant growth and development. We also found that the expression of NtGASA genes were mostly regulated by abscisic and gibberellic acid, signifying their roles in the two phytohormone signaling pathways. Overall, these findings improve our understanding of NtGASA genes and provided useful information for further studies on their molecular functions.

GhGASA10-1 promotes the cell elongation in fiber development through the phytohormones IAA-induced

BACKGROUND

Cotton is an important cash crop. The fiber length has always been a hot spot, but multi-factor control of fiber quality makes it complex to understand its genetic basis. Previous reports suggested that OsGASR9 promotes germination, width, and thickness by GAs in rice, while the overexpression of AtGASA10 leads to reduced silique length, which is likely to reduce cell wall expansion. Therefore, this study aimed to explore the function of GhGASA10 in cotton fibers development.

RESULTS

To explore the molecular mechanisms underlying fiber elongation regulation concerning GhGASA10-1, we revealed an evolutionary basis, gene structure, and expression. Our results emphasized the conservative nature of GASA family with its origin in lower fern plants S. moellendorffii. GhGASA10-1 was localized in the cell membrane, which may synthesize and transport secreted proteins to the cell wall. Besides, GhGASA10-1 promoted seedling germination and root extension in transgenic Arabidopsis, indicating that GhGASA10-1 promotes cell elongation. Interestingly, GhGASA10-1 was upregulated by IAA at fiber elongation stages.

CONCLUSION

We propose that GhGASA10-1 may promote fiber elongation by regulating the synthesis of cellulose induced by IAA, to lay the foundation for future research on the regulation networks of GASA10-1 in cotton fiber development.

Glutathione produced by γ-glutamyl cysteine synthetase acts downstream of hydrogen to positively influence lateral root branching

Hydrogen gas (H₂) mediation of lateral root (LR) branching was previously described. However, related signaling pathway is largely unexplored. In this study, we discovered that application with H₂ using hydrogen-rich water, mimicking the responses of exogenous glutathione (GSH), not only enhanced GSH synthesis, but also induced tomato LR development. The changes in the transcripts of auxin signaling-related genes and cell cycle regulatory genes were matched with above phenotypes. The addition of H₂ could trigger higher transcript levels of SlGSH1 and SlGSH2, encoding γ-glutamylcysteine synthetase (γ-ECS) and glutathione synthetase (GS), confirming the stimulation of GSH synthesis. These responses were greatly abolished when the inhibitor of γ-ECS was applied. The inhibition in lateral root primordium development, especially in emergence stage, was also observed. Genetic evidence revealed that the defects in GSH production and lateral rooting in Arabidopsis cad2-1, a γ-ECS defective mutant, were obviously abolished in the presence of GSH compared to those in the presence of H₂. Further evidence revealed that mRNA levels of target genes elicited by H₂ in wild-type, were differentially impaired in mutant plants. Together, above data clearly demonstrated that γ-ECS-dependent GSH production might be closely associated with H₂ control of LR branching.

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.

A genome-wide approach to the comprehensive analysis of GASA gene family in Glycine max

A vital role of short amino acid gene family, gibberellic acid stimulated arabidopsis (GASA), has been reported in plant growth and development. Although, little information is available about these cysteine rich short proteins in different plant species and this is the first comprehensive approach to exploit available genomic data and to analyze the GASA family in G. max. The phylogenetic and sequence composition analysis distributed the 37 identified GmGASA genes into three groups. Further investigation of the tissue expression pattern, phylogenetic analysis, motif, gene structure, chromosome distributions, duplication patterns, positive-selection pressure and cis-element analysis of 37 GmGASA genes. A conserved GASA domain was found in all identified GmGASA genes and exhibited similar characteristics. The online gene expression profile based analysis of GmGASA genes reveled that these genes were highly expressed in almost all soybean parts and some have high expression in flower which indicates that GmGASA genes displayed special or distinct expression pattern among different tissues. The segmental duplication was found in five pairs from 37 GmGASA genes and was distributed on 15 different chromosomes. The Ka/Ks ratio of 5 pairs of segmentally duplicated gene indicated that after the occurrence of duplication events, the duplicated gene pairs were purified and selected after restrictive functional differentiation. This investigated study of GmGASA gene will useful to support the statement about GASA genes role during flower induction in flowering plants.

A systematic in silico prediction of gibberellic acid stimulated GASA family members: A novel small peptide contributes to floral architecture and transcriptomic changes induced by external stimuli in rice

The GASA (GA-stimulated Arabidopsis) gene family is highly specific to plants, signifying a crucial role in plant growth and development. Herein, we retrieved 119 GASA genes in 10 different plant species in two major lineages (monocots and eudicots). Further, in the phylogenetic tree we classified these genes into four well-conserved subgroups. All the proteins contain a conserved GASA domain with similar characteristics and a highly specific 12-cysteine residue of the C-terminus position. According to the global microarray data and qRT-PCR based analysis, the OsGASA gene family was dominantly expressed in the seedling and transition phase of floral stages. Despite this, OsGASA genes profoundly contribute to rice grain size and length, whereas the highest abundance of transcript level was noticed in stage-2 (Inf 6, 3.0-cm-long spikelet) and stage-3 (Inf 7, 5.0-cm-long spikelet) under GA treatment during panicle formation. Additionally, the maximum expression level of these genes was recorded in response to GA and ABA in young seedlings. Further, in response to abiotic stresses, OsGASA1/8/10 was up- regulated by salt, OsGASA2/5/7 by drought, OsGASA3/6 by cold, and OsGASA4/9 by heat stress. With the exception of OsGASA4, the higher transcription levels of all the other GASA genes were induced by Cd and Cr metal stresses (8-10 fold changes) at various time points. Finally, the GO ontology analysis of GASAs revealed the biological involvement in the GA-mediated signaling pathway and abiotic stresses. Prominently, most of these proteins are localized in cellular components such as the cell wall and extracellular region, where the molecular functions such as ATP binding and protein binding were observed. These results imply that GASAs are significantly involved in rice panicle developmental stages, responses to external stimuli, and hormones.

Transcriptome Analyses from Mutant Salvia miltiorrhiza Reveals Important Roles for SmGASA4 during Plant Development

Salvia miltiorrhiza (S. miltiorrhiza) is an important Chinese herb that is derived from the perennial plant of Lamiaceae, which has been used to treat neurasthenic insomnia and cardiovascular disease. We produced a mutant S. miltiorrhiza (MT), from breeding experiments, that possessed a large taproot, reduced lateral roots, and defective flowering. We performed transcriptome profiling of wild type (WT) and MT S. miltiorrhiza using second-generation Illumina sequencing to identify differentially expressed genes (DEGs) that could account for these phenotypical differences. Of the DEGs identified, we investigated the role of SmGASA4, the expression of which was down-regulated in MT plants. SmGASA4 was introduced into Arobidopsis and S. militiorrhiza under the control of a CaMV35S promoter to verify its influence on abiotic stress and S. miltiorrhiza secondary metabolism biosynthesis. SmGASA4 was found to promote flower and root development in Arobidopsis. SmGASA4 was also found to be positively regulated by Gibberellin (GA) and significantly enhanced plant resistance to salt, drought, and paclobutrazol (PBZ) stress. SmGASA4 also led to the up-regulation of the genes involved in salvianolic acid biosynthesis, but inhibited the expression of the genes involved in tanshinone biosynthesis. Taken together, our results reveal SmGASA4 as a promising candidate gene to promote S. miltiorrhiza development.

The Arabidopsis GASA10 gene encodes a cell wall protein strongly expressed in developing anthers and seeds

The Arabidopsis GASA10 gene encodes a GAST1-like (Gibberellic Acid-Stimulated) protein. Reporter gene analysis identified consistent expression in anthers and seeds. In anthers expression was developmentally regulated, first appearing at stage 7 of anther development and reaching a maximum at stage 11. Strongest expression was in the tapetum and developing microspores. GASA10 expression also occurred throughout the seed and in root vasculature. GASA10 was shown to be transported to the cell wall. Using GASA1 and GASA6 as positive controls, gibberellic acid was found not to induce GASA10 expression in Arabidopsis suspension cells. Overexpression of GASA10 (35S promoter-driven) resulted in a reduction in silique elongation. GASA10 shares structural similarities to the antimicrobial peptide snakin1, however, purified GASA10 failed to influence the growth of a variety of bacterial and fungal species tested. We propose cell wall associated GASA proteins are involved in regulating the hydroxyl radical levels at specific sites in the cell wall to facilitate wall growth (regulating cell wall elongation).

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.

Involvement of glutathione in β-cyclodextrin-hemin complex-induced lateral root formation in tomato seedlings

β-cyclodextrin-hemin complex (β-CDH) was shown to induce lateral root (LR) formation in tomato. However, the molecular mechanism is still elusive. In this report, the role of reduced glutathione (GSH) in the induction of lateral root triggered by β-CDH was investigated. Similar to the responses of β-CDH, exogenously applied with 0.1 mΜ GSH not only increased endogenous GSH content determined by spectrophotography and the monochlorobimane (MCB)-dependent fluorescent analysis, but also induced, thereafter, LR formation. Meanwhile, both β-CDH- and GSH-induced lateral root primordia (LRP) exhibited a similar accelerated anatomic structure. Above inducible responses were blocked significantly when the _L-buthionine-(S,R)-sulfoximine (BSO), a potent and specific inhibitor of the enzyme catalyzing the first step of GSH biosynthesis, was separately applied. Upon β-CDH treatment, the changes of endogenous GSH content determined by spectrophotography and fluorescent analysis were consistent with the transcripts of two GSH synthetic genes, GSH1 and GSH2 encoding γ-glutamyl cysteine synthetase and glutathione synthetase, respectively. Exogenously applied with β-CDH could rescue N-1-naphthylphthalamic acid (NPA; IAA depletion)-triggered inhibition of LR formation. Further molecular evidence revealed that both β-CDH and GSH modulated gene expression of cell cycle regulatory genes (CYCA2;1, CYCA3;1, CYCD3;1, and CDKA1) and auxin signaling genes (ARF7 and RSI-1), six marker genes responsible for LR formation. By contrast, above changes were sensitive to the co-treatment with BSO. All together, these results suggest a role for GSH in the regulation of tomato LR development triggered by β-CDH.

Molecular and cellular characterization of GA-Stimulated Transcripts GASA4 and GASA6 in Arabidopsis thaliana

GA and ABA play antagonistic roles in numerous cellular processes essential for growth, development, and stress responses. GASA4 and GASA6 belong to a family of GA-Stimulated transcripts in Arabidopsis, known as GA-inducible and ABA-repressible. We have found that GASA4 and GASA6 expression is likely mediated through a repressor of GA responses, GA INSENSITIVE (GAI) protein. Moreover, GASA4 and GASA6 are in general up regulated by growth hormones (auxin, BR, cytokinin, and GA) and down regulated by stress hormones (ABA, JA, and SA), indicating a role of GASA4 and GASA6 in hormone crosstalk. Genetic analyses show that suppression of both GASA4 and GASA6 causes late flowering, while over-expression of GASA6 causes early flowering in Arabidopsis. GASA family members encode small polypeptides sharing common structural features: an N-terminal signal peptide, a highly divergent intermediate region, and a conserved C-terminal domain containing 12 conserved cysteines. Despite the presence of a signal peptide, it has not been determined whether or not GASA4 and GASA6 can be processed in vivo. By using imaging and immunological analyses, we show that the N-terminal signal peptide is cleaved as predicted, and the cleavage is important for proper sub-cellular localization of GASA4 and GASA6.

β-Cyclodextrin-hemin complex-induced lateral root formation in tomato: involvement of nitric oxide and heme oxygenase 1

β-Cyclodextrin-hemin complex-induced tomato lateral root formation was associated with nitric oxide and heme oxygenase 1 by modulating cell cycle regulatory genes. β-Cyclodextrin-hemin complex (β-CDH), a complex by combining β-cyclodextrin (β-CD) with hemin, a heme oxygenase 1 (HO1) inducer, was a trigger of cucumber adventitious root formation by enhancing HO1 gene expression. In this report, our results identified the previously unknown function of β-CDH in plants: the inducer of tomato lateral root (LR) formation. β-CDH-triggered LR formation is hemin-specific, since β-CD failed to induce LR development. Because nitric oxide (NO) is involved in LR formation, the correlation of β-CDH with NO and HO1 was investigated. Our analysis suggested that β-CDH induced an increase in endogenous NO production, followed by up-regulation of tomato HO1 gene and LR formation, all of which were mimicked by hemin and two NO-releasing compounds (SNP and GSNO). The induction of HO1 gene expression and LR formation triggered by β-CDH or hemin were significantly blocked by an inhibitor of HO1. Further results revealed that both β-CDH- and SNP-stimulated HO1 gene expression and thereafter LR formation were sensitive to the removal of NO with a potent NO scavenger, and the responses of SNP were significantly blocked by an inhibitor of HO1. Molecular evidence illustrated that representative cell cycle regulatory genes, including SlCDKA1, SlCYCA3;1, SlCYCA2;1, and SlCYCD3;1, were significantly up-regulated by β-CDH and SNP, but obviously blocked when seedlings were co-treated with the scavenger of NO or the inhibitor of HO1. In summary, our physiological and molecular evidence demonstrated that both NO and HO1 were involved in the β-CDH-induced LR formation with, at least partially, HO1 acting downstream of NO signaling.

Heme oxygenase-1 is involved in sodium hydrosulfide-induced lateral root formation in tomato seedlings

By using pharmacological and molecular approaches, we discovered the involvement of HO-1 in NaHS-induced lateral root formation in tomato seedlings. Heme oxygenase-1 (HO-1) and hydrogen sulfide (H2S) regulate various responses to abiotic stress and root development, but their involvement in the simultaneous regulation of plant lateral root (LR) formation is poorly understood. In this report, we observed that the exogenously applied H2S donor sodium hydrosulfide (NaHS) and the HO-1 inducer hemin induce LR formation in tomato seedlings by triggering intracellular signaling events involving the induction of tomato HO-1 (SlHO-1), and the modulation of cell cycle regulatory genes, including the up-regulation of SlCDKA;1 and SlCYCA2;1, and simultaneous down-regulation of SlKRP2. The response of NaHS in the induction of LR formation was impaired by the potent inhibition of HO-1, which was further blocked when 50 % saturation of carbon monoxide (CO) aqueous solution, one of the catalytic by-products of HO-1, was added. Further molecular evidence revealed that the NaHS-modulated gene expression of cell cycle regulatory genes was sensitive to the inhibition of HO-1 and reversed by cotreatment with CO. The impairment of LR density and length as well as lateral root primordia number, the decreased tomato HO-1 gene expression and HO activity caused by an H2S scavenger hypotaurine were partially rescued by the addition of NaHS, hemin and CO (in particular). Together, these results revealed that at least in our experimental conditions, HO-1 might be involved in NaHS-induced tomato LR formation. Additionally, the use of NaHS and hemin compounds in crop root organogenesis should be explored.

Post-embryonic root organogenesis in cereals: branching out from model plants

The root architecture of higher plants is amazingly diverse. In this review, we compare the lateral root developmental programme in cereals and Arabidopsis thaliana. In cereals, cells in the endodermis are recruited to form the new root cap and overlying cortical cells divide to facilitate the emergence of the lateral root primordium. The TIR1/ABF2 auxin receptors and the AUX/IAA, ARF, and LBD transcriptional regulatory proteins are conserved in cereals and Arabidopsis. Several elements of this regulatory network are common to lateral and crown roots in cereals. Also, the ground meristem from which crown roots differentiate shows similarities with the root pericycle. Studies in cereals promise to give complementary insights into the mechanisms regulating the development of post-embryonic roots in plants.

Cotton GASL genes encoding putative gibberellin-regulated proteins are involved in response to GA signaling in fiber development

GAST (GA-stimulated transcript)-like genes have been reported as targets of GA regulation in some plant species. In this study, we isolated seven GAST-like cDNAs from cotton (Gossypium hirsutum) cDNA libraries (designated as GhGASL1-GhGASL7). Meanwhile, the genomic DNA clones corresponding to the seven GhGASL genes were isolated by using PCR amplification technique. Analysis of gene structure revealed that four genes (GhGASL1/3/5/6) contain two exons and one intron, while the rest have four exons and three introns. All of the deduced GhGASL proteins contain a putative signal peptide in the N-terminus and a conservative cysteine-rich C-terminal domain. Quantitative RT-PCR analysis indicated that the seven GhGASL genes are differentially expressed in cotton tissues. Among them, GhGASL1/4/7 were predominantly expressed in cotyledons, while the transcripts of GhGASL2/5 were preferentially accumulated at hypocotyls. GhGASL3 mRNA was largely accumulated in fibers, while GhGASL6 transcripts were mainly detected in ovules. Furthermore, GhGASL2/3/5 displayed a relatively high expression levels during early fiber elongation stages, and were regulated by GA. These data suggested that GhGASL genes may be involved in fiber elongation and in response to GA signaling during fiber development.

Expression profiling of tomato pre-abscission pedicels provides insights into abscission zone properties including competence to respond to abscission signals

BACKGROUND

Detachment of plant organs occurs in abscission zones (AZs). During plant growth, the AZ forms, but does not develop further until the cells perceive abscission-promoting signals and initiate detachment. Upon signal perception, abscission initiates immediately; if there is no signal, abscission is not induced and the organ remains attached to the plant. However, little attention has been paid to the genes that maintain competence to respond to the abscission signal in the pre-abscission AZ. Recently, we found that the tomato (Solanum lycopersicum) transcription factors BLIND (Bl), GOBLET (GOB), Lateral suppressor (Ls) and a tomato WUSCHEL homologue (LeWUS) are expressed specifically in pre-abscission tissue, the anthesis pedicel AZs. To advance our understanding of abscission, here we profiled genome-wide gene expression in tomato flower pedicels at the pre-abscission stage.

RESULTS

We examined the transcriptomes of three tomato flower pedicel regions, the AZ and flanking proximal- (Prox) and distal- (Dis) regions, and identified 89 genes that were preferentially expressed in the AZ compared to both Prox and Dis. These genes included several transcription factors that regulate apical or axillary shoot meristem activity. Also, genes associated with auxin activity were regulated in a Prox-Dis region-specific manner, suggesting that a gradient of auxin exists in the pedicel. A MADS-box gene affecting floral transition was preferentially expressed in the Prox region and other MADS-box genes for floral organ identification were preferentially expressed in Dis, implying that the morphologically similar Prox and Dis regions have distinct identities. We also analyzed the expression of known regulators; in anthesis pedicels, Bl, GOB, Ls and LeWUS were expressed in the vascular cells of the AZ region. However, after an abscission signal, Bl was up-regulated, but GOB, Ls and LeWUS were down-regulated, suggesting that Bl may be a positive regulator of abscission, but the others may be negative regulators.

CONCLUSIONS

This study reveals region-specific gene expression in tomato flower pedicels at anthesis and identifies factors that may determine the physiological properties of the pre-abscission pedicel. The region-specific transcriptional regulators and genes for auxin activity identified here may prevent flower abscission in the absence of signal or establish competence to respond to the abscission signal.

Role of the CPC sequence in the antioxidant activity of GcGAST protein in E.coli

Gibberellic acid stimulated transcriptional protein from Gymnadenia conopsea (GcGAST) is a novel member of GA-induced cysteine-rich protein family, which shared 12 highly conserved cysteine residues with other members in C-terminal domain. In the present paper, the recombinant plasmid, as well as two mutants Serine-Proline-Cysteine (SPC) and Cysteine-Proline-Serine (CPS), were constructed to investigate for the first time the effects of the cysteines in Cysteine-Proline-Cysteine (CPC) sequence on the antioxidant activity of GcGAST protein. It was found that E.coli expressing wt GcGAST exhibited significant resistance against exogenous H(2)O(2). Similar phenomenon was observed for E.coli harboring SPC mutant. In contrast, the host cell overexpressing CPS mutant became more sensitive to H(2)O(2). Some studies on the level of inclusion body revealed that wt GcGAST and SPC mutant embedded in Inclusion bodies (IB) could effectively eliminate H(2)O(2), whereas the mutagenesis to Ser of the second Cys residue in CPC sequence gave rise to the compete loss of H(2)O(2)-eliminating ability. Fourier transform Infrared spectroscopy analysis indicated that the IB of CPS mutant contained more β-sheet secondary structure than wt and SPC mutant. Non-reducing SDS-PAGE combined western-blotting analysis revealed that the disulfide bonds were important for the formation of IBs of wt GcGAST and SPC mutant, whereas non-reducing SDS-PAGE of resolubilized IBs showed that hydrophobic interaction favored the aggregation of IBs in CPS mutant. Taken together, these results suggested that GcGAST possessed antioxidant activity in the level of IB, which made some contribution to cellular resistance to H(2)O(2). More importantly, the second cysteine residue in CPC sequence was more essential for its antioxidant biological function.

Snakin/GASA proteins: involvement in hormone crosstalk and redox homeostasis

Snakin/GASA proteins are widely distributed among plant species. They are expressed in different plant organs with high tissue and temporal specificity, and their subcellular localization varies among the different members. Interestingly, all of them maintain 12 cysteines of the C-terminus in highly conserved positions of the aminoacid sequences that are essential for their biochemical activity and probably responsible for their protein structure. Despite their common features, their functions are not completely elucidated and little is known about their mode of action. This review focuses on the current knowledge about this intriguing family of peptides and advances comprising gene regulation analyses, expression pattern studies and phenotypic characterization of mutants and transgenic plants. Furthermore, we discuss the roles of Snakin/GASA proteins in several aspects of plant development, plant responses to biotic or abiotic stress and their participation in hormone crosstalk and redox homeostasis.

GsGASA1 mediated root growth inhibition in response to chronic cold stress is marked by the accumulation of DELLAs

Low, but not freezing temperatures are a major factor limiting plant vegetative growth and development. It is not clear what signaling mechanism is used to limit plant growth in response to chronic low temperatures, thus it is important to continue to isolate and characterize genes whose activity/expression correlate well with cold responses. In this study, a novel GASA gene was isolated from Glycine soja and named GsGASA1. Quantitative real-time PCR analysis indicated that GsGASA1 expression responded to exogenous gibberellic acid (GA) and abscisic acid (ABA) treatments. Compared with wild-type plants under long-term cold treatment, the constitutive expression of GsGASA1 in transgenic Arabidopsis plants enhanced the inhibition of root elongation, while also increasing the transcript levels of RGL2 and RGL3, two of five DELLA genes in Arabidopsis. DELLA is a class of transcriptional regulators in GA signaling pathway restraining plant growth. Our results imply that GsGASA1 participates in chronic cold-induced root growth inhibition with the accumulation of DELLA genes. Lastly, a subcellular localization study using a yellow fluorescent protein (YFP) fusion protein indicated that GsGASA1 was localized to the plasma membrane, cytoplasm and nucleus.

The Arabidopsis cysteine-rich protein GASA4 promotes GA responses and exhibits redox activity in bacteria and in planta

Although the gibberellin (GA) signaling pathway has been elucidated, very little is known about the steps linking first transcriptional activation to physiological responses. Among the few identified GA-induced genes are the plant-specific GAST1-like genes, which encode small proteins with a conserved cysteine-rich domain. The role of these proteins in plant development and GA responses is not yet clear. The Arabidopsis GAST1-like gene family consists of 14 members, GASA1-14. Here we show that over-expression of the GA-induced GASA4 gene in Arabidopsis promoted GA responses such as flowering and seed germination. Suppression of several GASA genes using synthetic microRNA (miR(GASA) ) also promoted seed germination. This was probably caused by suppression of GASA5, which acts as a repressor of GA responses. Previously, we proposed that GAST1-like proteins are involved in redox reactions via their cysteine-rich domain. The results of this study support this hypothesis, as over-expression of GASA4 suppressed ROS accumulation and the transgenic seeds were partially resistant to the NO donor sodium nitroprusside (SNP). Moreover, Escherichia coli expressing intact GASA4 or a truncated version containing only the cysteine-rich domain were resistant to SNP. Mutated GASA4, in which conserved cysteines were replaced by alanines, lost its redox activity and the ability to promote GA responses, suggesting that the two functions are linked. We propose that GA induces some GAST1-like genes and suppresses others to regulate its own responses. We also suggest that the encoded proteins regulate the redox status of specific components to promote or suppress these responses.

The Gibberellic Acid Stimulated-Like gene family in maize and its role in lateral root development

In an approach to study lateral root development in monocots, genome-wide searches for homologs of the Gibberellic Acid Stimulated Transcript-like (GAST-like) gene family in rice (Oryza sativa) and maize (Zea mays) were carried out. Six novel GAST-like genes in rice and 10 members of the gene family in maize, which were designated ZmGSL (for Z. mays Gibberellic Acid Stimulated-Like), were identified. The ZmGSL family encodes small proteins of 75 to 128 amino acids, which are characterized by a conserved 59 to 64 amino acid C-terminal domain. Within this domain, 17 amino acids, including 12 cysteines, are perfectly conserved. The transcript of the ZmGSL1 gene is differentially spliced into the alternative variants ZmGSL1a and ZmGSL1b, the latter of which is translated into a premature protein that lacks the C-terminal domain. The presence of an additional N-terminal cleavable signal sequence in eight of the 10 ZmGSL proteins suggests that they are secreted into the extracellular matrix. In-depth root-specific gene expression analyses carried out in the wild type and the lateral root mutants lrt1 and rum1 suggest a role for ZmGSL genes in early lateral root development, which is likely regulated by gibberellic acid. Expression patterns of ZmGSL1a and ZmGSL1b propose antagonistic functions of these splice variants during early lateral root formation.

Low phosphate signaling induces changes in cell cycle gene expression by increasing auxin sensitivity in the Arabidopsis root system

Lateral root development is an important morphogenetic process in plants, which allows the modulation root architecture and substantially determines the plant's efficiency for water and nutrient uptake. Postembryonic root development is under the control of both endogenous developmental programs and environmental stimuli. Nutrient availability plays a major role among environmental signals that modulate root development. Phosphate (Pi) limitation is a constraint for plant growth in many natural and agricultural ecosystems. Plants possess Pi-sensing mechanisms that enable them to respond and adapt to conditions of limited Pi supply, including increased formation and growth of lateral roots. Root developmental modifications are mainly mediated by the plant hormone auxin. Recently we showed that the alteration of root system architecture under Pi-starvation may be mediated by modifications in auxin sensitivity in root cells via a mechanism involving the TIR1 auxin receptor. In this addendum, we provide additional novel evidence indicating that the low Pi pathway involves changes in cell cycle gene expression. It was found that Pi deprivation increases the expression of CDKA, E2Fa, Dp-E2F and CyCD3. In particular, E2Fa, Dp-E2F and CyCD3 genes were specifically upregulated by auxin in Pi-deprived Arabidopsis seedlings that were treated with the auxin transport inhibitor NPA, indicating that cell cycle modulation by low Pi signaling is independent of auxin transport and dependent on auxin sensitivity in the root.

OsGSR1 is involved in crosstalk between gibberellins and brassinosteroids in rice

Gibberellins (GAs) and brassinosteroids (BRs), two growth-promoting phytohormones, regulate many common physiological processes. Their interactions at the molecular level remain unclear. Here, we demonstrate that OsGSR1, a member of the GAST (GA-stimulated transcript) gene family, is induced by GA and repressed by BR. RNA interference (RNAi) transgenic rice plants with reduced OsGSR1 expression show phenotypes similar to plants deficient in BR, including short primary roots, erect leaves and reduced fertility. The OsGSR1 RNAi transgenic rice shows a reduced level of endogenous BR, and the dwarf phenotype could be rescued by the application of brassinolide. The yeast two-hybrid assay revealed that OsGSR1 interacts with DIM/DWF1, an enzyme that catalyzes the conversion from 24-methylenecholesterol to campesterol in BR biosynthesis. These results suggest that OsGSR1 activates BR synthesis by directly regulating a BR biosynthetic enzyme at the post-translational level. Furthermore, OsGSR1 RNAi plants show a reduced sensitivity to GA treatment, an increased expression of the GA biosynthetic gene OsGA20ox2, which is feedback inhibited by GA signaling, and an elevated level of endogenous GA: together, these suggest that OsGSR1 is a positive regulator of GA signaling. These results demonstrate that OsGSR1 plays important roles in both BR and GA pathways, and also mediates an interaction between the two signaling pathways.

PRGL: A cell wall proline-rich protein containning GASA domain in Gerbera hybrida

PRPs (proline-rich proteins) are a group of cell wall proteins characterized by their proline and hydroproline-rich repetitive peptides. The expression of PRPs in plants is stimulated by wounding and environmental stress. GASA (gibberellic acid stimulated in Arabidopsis) proteins are small peptides sharing a 60 amino acid conserved C-terminal domain containing twelve invariant cysteine residues. Most of GASAs reported are localized to apoplasm or cell wall and their expression was regulated by gibberellins (GAs). It has been reported that, in French bean, these two proteins encoding by two distinct genes formed a two-component chitin-receptor involved in plant-pathogen interactions when plant was infected. We cloned a full-length cDNA of PRGL (proline-rich GASA-like) gene which encodes a protein containing both PRP and GASA-like domains. It is demonstrated that PRGL is a new protein with characteristics of PRP and GASA by analyzing its protein structure and gene expression.

Molecular and phenotypic profiling from the base to the crown in maritime pine wood-forming tissue

Environmental, developmental and genetic factors affect variation in wood properties at the chemical, anatomical and physical levels. Here, the phenotypic variation observed along the tree stem was explored and the hypothesis tested that this variation could be the result of the differential expression of genes/proteins during wood formation. Differentiating xylem samples of maritime pine (Pinus pinaster) were collected from the top (crown wood, CW) to the bottom (base wood, BW) of adult trees. These samples were characterized by Fourier transform infrared spectroscopy (FTIR) and analytical pyrolysis. Two main groups of samples, corresponding to CW and BW, could be distinguished from cell wall chemical composition. A genomic approach, combining large-scale production of expressed sequence tags (ESTs), gene expression profiling and quantitative proteomics analysis, allowed identification of 262 unigenes (out of 3512) and 231 proteins (out of 1372 spots) that were differentially expressed along the stem. A good relationship was found between functional categories from transcriptomic and proteomic data. A good fit between the molecular mechanisms involved in CW-BW formation and these two types of wood phenotypic differences was also observed. This work provides a list of candidate genes for wood properties that will be tested in forward genetics.

Plasticity of maritime pine (Pinus pinaster) wood-forming tissues during a growing season

The seasonal effect is the most significant external source of variation affecting vascular cambial activity and the development of newly divided cells, and hence wood properties. Here, the effect of edapho-climatic conditions on the phenotypic and molecular plasticity of differentiating secondary xylem during a growing season was investigated. Wood-forming tissues of maritime pine (Pinus pinaster) were collected from the beginning to the end of the growing season in 2003. Data from examination of fibre morphology, Fourier-transform infrared spectroscopy (FTIR), analytical pyrolysis, and gas chromatography/mass spectrometry (GC/MS) were combined to characterize the samples. Strong variation was observed in response to changes in edapho-climatic conditions. A genomic approach was used to identify genes differentially expressed during this growing season. Out of 3512 studied genes, 19% showed a significant seasonal effect. These genes were clustered into five distinct groups, the largest two representing genes over-expressed in the early- or late-wood-forming tissues, respectively. The other three clusters were characterized by responses to specific edapho-climatic conditions. This work provides new insights into the plasticity of the molecular machinery involved in wood formation, and reveals candidate genes potentially responsible for the phenotypic differences found between early- and late-wood.

GASA4, one of the 14-member Arabidopsis GASA family of small polypeptides, regulates flowering and seed development

Members of the plant-specific gibberellic acid-stimulated Arabidopsis (GASA) gene family play roles in hormone response, defense and development. We have identified six new Arabidopsis GASA genes, bringing the total number of family members to 14. Here we show that these genes all encode small polypeptides that share the common structural features of an N-terminal putative signal sequence, a highly divergent intermediate region and a conserved 60 amino acid C-terminal domain containing 12 conserved cysteine residues. Analysis of promoter::GUS (beta-glucuronidase) transgenic plants representing six different GASA loci reveals that the promoters are activated in a variety of stage- and tissue-specific patterns during development, indicating that the GASA genes are involved in diverse processes. Characterization of GASA4 shows that the promoter is active in the shoot apex region, developing flowers and developing embryos. Phenotypic analyses of GASA4 loss-of-function and gain-of-function lines indicate that GASA4 regulates floral meristem identity and also positively affects both seed size and total seed yield.

Two OsGASR genes, rice GAST homologue genes that are abundant in proliferating tissues, show different expression patterns in developing panicles

Two different types of genes for rice GA-stimulated transcript (GAST) homologue genes, Oryza sativa GA-stimulated transcript-related gene 1 (OsGASR1) and gene 2 (OsGASR2), were found. Both OsGASR proteins contain a cysteine-rich domain highly conserved among GAST family proteins in their C-terminal regions. Gibberellin A3 (GA3) stimulated expression of both OsGASRs in the wild-type Nipponbare and GA3 synthesis-deficient mutant. Expression of both OsGASRs apparently increased when cell proliferation entered the logarithmic phase, and rapidly reduced when cell proliferation was temporarily halted. RT-PCR analysis indicated different expression patterns of these genes in developing panicles. OsGASR1 was limitedly but strongly expressed in florets while OsGASR2 was expressed in both florets and branches. In situ hybridization showed that they were strongly expressed in the root apical meristem (RAM) and shoot apical meristem (SAM), but little signals were detected in mature leaves. Transient expression of OsGASR-GFP fusion proteins in onion epidermal cells revealed that both OsGASR proteins localized to the apoplasm or cell wall. These results suggest that OsGASR1 and OsGASR2 were involved in cell division and might play diverse roles in differentation of panicles.

Comparative serial analysis of gene expression of transcript profiles of tomato roots infected with cyst nematode

We analyzed global transcripts for tomato roots infected with the cyst nematode Globodera rostochiensis using serial analysis of gene expression (SAGE). SAGE libraries were made from nematode-infected roots and uninfected roots at 14 days after inoculation, and the clones including SAGE tags were sequenced. Genes were identified by matching the SAGE tags to tomato expressed sequence tags and cDNA databases. We then compiled a list of numerous genes according to the mRNA levels that were altered after cyst nematode infection. Our SAGE results showed significant changes in expression of many unreported genes involved in nematode infection. Of these, for discussion we selected five SAGE tags of RSI-1, BURP domain-containing protein, hexose transporter, P-rich protein, and PHAP2A that were activated by cyst nematode infection. Over 20% of the tags that were upregulated in the infected root have unknown functions (non-annotated), suggesting that we can obtain information on previously unreported and uncharacterized genes by SAGE. We can also obtain information on previously reported genes involved in nematode infection (e.g., multicystatin, peroxidase, catalase, pectin esterase, and S-adenosylmethionine transferase). To evaluate the validity of our SAGE results, seven genes were further analyzed by semiquantitative reverse transcriptase-polymerase chain reaction and Northern blot hybridization; the results agreed well with the SAGE data.

The gibberellin-induced, cysteine-rich protein GIP2 from Petunia hybrida exhibits in planta antioxidant activity

Numerous GAST-like genes have been identified in various plant species. All code for small proteins with a conserved C-terminal region in which 12 cysteines are located in exactly the same positions. We have previously identified five gibberellin (GA)-induced GAST1-like genes in petunia, GIP1-5. GIP2 is expressed in elongating zones, and its suppression in transgenic petunia plants inhibits stem elongation, suggesting a role for the protein in GA-induced cell growth. However, nothing is known about the biochemical activity of GIP2 or any other GAST-like protein. As all contain putative catalytic disulfide bonds (putative redox-active cysteines), we speculated that they might be involved in redox regulation. Expression analysis of GIP2, GIP4 and GIP5 revealed that they are induced by H(2)O(2). To study whether GIP2 modulates H(2)O(2) levels, we generated transgenic petunia plants expressing GIP2 under the regulation of the ubiquitous CaMV 35S promoter. The transgene reduced H(2)O(2) levels in leaves following wounding. It also reduced the levels of H(2)O(2) in guard cells following osmotic stress and ABA treatments, leading to the suppression of stomatal closure. In addition, the transgene promoted stem and corolla elongation. As reactive oxygen species (ROS) are involved in cell elongation, we suggest that GIP2 affects growth by regulating the levels of ROS. As all known GAST-like proteins contain putative redox-active cysteines, they may all act as antioxidants.

Lateral root initiation or the birth of a new meristem

Root branching happens through the formation of new meristems out of a limited number of pericycle cells inside the parent root. As opposed to shoot branching, the study of lateral root formation has been complicated due to its internal nature, and a lot of questions remain unanswered. However, due to the availability of new molecular tools and more complete genomic data in the model species Arabidopsis, the probability to find new and crucial elements in the lateral root formation pathway has increased. Increasingly more data are supporting the idea that lateral root founder cells become specified in young root parts before differentiation is accomplished. Next, pericycle founder cells undergo anticlinal asymmetric, divisions followed by an organized cell division pattern resulting in the formation of a new organ. The whole process of cell cycle progression and stimulation of the molecular pathway towards lateral root initiation is triggered by the plant hormone auxin. In this review, we aim to give an overview on the developmental events taking place from the very early specification of founder cells in the pericycle until the first anticlinal divisions by combining the knowledge originating from classical physiology studies with new insights from genetic-molecular analyses. Based on the current knowledge derived from recent genetic and developmental studies, we propose here a hypothetical model for LRI.

Novel markers of xylogenesis in zinnia are differentially regulated by auxin and cytokinin

The characterization of in vitro xylogenic cultures of zinnia (Zinnia elegans) has led to major discoveries in the understanding of xylem formation in plants. We have constructed and characterized a subtractive library from zinnia cultures enriched in genes that are specifically expressed at the onset of secondary wall deposition and tracheary element (TE) programmed cell death. This Late Xylogenesis Library (LXL) consisted of 236 nonredundant cDNAs, 77% of which encoded novel sequences in comparison with the 17,622 expressed sequence tag sequences publicly available. cDNA arrays were constructed to examine dynamic global gene expression during the course of TE formation. As a first step in dissecting auxin and cytokinin signaling during TE differentiation, macroarrays were probed with cDNAs from cells cultured in different hormonal conditions. Fifty-one percent of the LXL genes were induced by either auxin or cytokinin individually, the large majority by auxin. To determine the potential involvement of these categories of genes in TE differentiation, multiplex in situ-reverse transcription-PCR was performed on cells for two genes encoding putative cell wall proteins: Gibberellin stimulated transcript-1, induced by auxin alone, and expansin 5, induced by cytokinin alone. All transcriptionally active TEs expressed both genes, indicating that, although these genes may not be considered as specific markers for TE differentiation per se, they are nevertheless an integral part of TE differentiation program. Among the non-TE population, four different gene expression-based cell types could be distinguished. Together, these results demonstrate the underlying complexity of hormonal perception and the existence of several different cell types in in vitro TE cell cultures.

AtMYB32 is required for normal pollen development in Arabidopsis thaliana

AtMYB32 gene is a member of the R2R3 MYB gene family coding for transcription factors in Arabidopsis thaliana. Its expression pattern was analysed using Northern blotting, in situ hybridization and promoter-GUS fusions. AtMYB32 is expressed in many tissues, but most strongly in the anther tapetum, stigma papillae and lateral root primordia. AtMYB32-GUS was induced in leaves and stems following wounding, and in root primordia by auxin. T-DNA insertion populations were screened and two insertion mutants were identified, both of which were partially male sterile, more than 50% of the pollen grains being distorted in shape and lacking cytoplasm. AtMYB4 is closely related to AtMYB32 and represses the CINNAMATE 4-HYDROXYLASE gene. Distorted pollen grains were produced in both AtMYB4 insertion mutant and overexpression lines. In an AtMYB32 insertion mutant, the transcript levels of the DIHYDROFLAVONOL 4-REDUCTASE and ANTHOCYANIDIN SYNTHASE genes decreased while the level of the CAFFEIC ACID 0-METHYLTRANSFERASE transcript increased. Change in the levels of AtMYB32 and AtMYB4 expression may influence pollen development by changing the flux along the phenylpropanoid pathways, affecting the composition of the pollen wall.

Expression profiling in Medicago truncatula identifies more than 750 genes differentially expressed during nodulation, including many potential regulators of the symbiotic program

In this study, we describe a large-scale expression-profiling approach to identify genes differentially regulated during the symbiotic interaction between the model legume Medicago truncatula and the nitrogen-fixing bacterium Sinorhizobium meliloti. Macro- and microarrays containing about 6,000 probes were generated on the basis of three cDNA libraries dedicated to the study of root symbiotic interactions. The experiments performed on wild-type and symbiotic mutant material led us to identify a set of 756 genes either up- or down-regulated at different stages of the nodulation process. Among these, 41 known nodulation marker genes were up-regulated as expected, suggesting that we have identified hundreds of new nodulation marker genes. We discuss the possible involvement of this wide range of genes in various aspects of the symbiotic interaction, such as bacterial infection, nodule formation and functioning, and defense responses. Importantly, we found at least 13 genes that are good candidates to play a role in the regulation of the symbiotic program. This represents substantial progress toward a better understanding of this complex developmental program.

GIP, a Petunia hybrida GA-induced cysteine-rich protein: a possible role in shoot elongation and transition to flowering

The Petunia hybrida GA-induced proteins (GIPs) belong to a large group of proteins identified in numerous plant species. These proteins share a similar C-terminal region containing 12 cysteine residues in conserved positions. To date, the function of these proteins remains unclear. We previously found that GIP1 expression coincides with cell elongation in stems and flowers and is induced by gibberellic acid (GA3). Transient expression of a GIP1:green fluorescent protein (GFP) fusion in tobacco bright yellow 2 (BY2) cells and immunoblot analyses suggest microsomal compartmentalization with possible endoplasmic reticulum (ER) localization. However, the polyclonal anti-GIP1 antibodies also reacted with proteins extracted from the cell wall. Three novel GIP homologs, GIP2, GIP4, and GIP5, were isolated. While GIP4, similar to GIP1, is putatively localized to the ER membrane, the cleavable hydrophobic N-terminal sequences of GIP2 and GIP5 suggest cell wall localization. GIP1 and GIP2 are expressed during cell elongation, whereas GIP4 and GIP5 are expressed during cell division; nevertheless, they all were induced by GA3. We generated transgenic petunia in which we repressed the putative cell wall protein GIP2. The transgenic plants exhibited late flowering and reduced stem elongation. These phenotypic alterations were found under low, but not moderate-high temperatures, suggesting functional redundancy under normal growth conditions. The expression pattern and cellular localization of GIP2, its regulation by GA, and the phenotype of the transgenic plants suggest a role in GA-mediated cell elongation and transition to flowering.

Snakin-1, a peptide from potato that is active against plant pathogens

A new type of antimicrobial peptide, snakin-1 (SN1), has been isolated from potato tubers and found to be active, at concentrations < 10 microM, against bacterial and fungal pathogens from potato and other plant species. The action of SN1 and potato defensin PTH1 was synergistic against the bacterium Clavibacter michiganensis subsp. sepedonicus and additive against the fungus Botrytis cinerea. Snakin-1 causes aggregation of both gram-positive and gram-negative bacteria. The peptide has 63 amino acid residues (M(r) 6,922), 12 of which are cysteines, and is unrelated to any previously isolated protein, although it is homologous to amino acid sequences deduced from cloned cDNAs that encode gibberellin-inducible mRNAs and has some sequence motifs in common with kistrin and other hemotoxic snake venoms. A degenerate oligonucleotide probe based on the internal sequence CCEECKC has been used to clone an SN1 cDNA. With the cDNA used as probe, one copy of the StSN1 gene per haploid genome has been estimated and expression of the gene has been detected in tubers, stems, axillary buds, and young floral buds. Expression levels in petals and carpels from fully developed flowers were much higher than in sepals and stamens. The expression pattern of gene StSN1 suggests that protein SN1 may be a component of constitutive defense barriers, especially those of storage and reproductive plant organs.

The diageotropica gene differentially affects auxin and cytokinin responses throughout development in tomato

The interactions between the plant hormones auxin and cytokinin throughout plant development are complex, and genetic investigations of the interdependency of auxin and cytokinin signaling have been limited. We have characterized the cytokinin sensitivity of the auxin-resistant diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) in a range of auxin- and cytokinin-regulated responses. Intact, etiolated dgt seedlings showed cross-resistance to cytokinin with respect to root elongation, but cytokinin effects on hypocotyl growth and ethylene synthesis in these seedlings were not impaired by the dgt mutation. Seven-week-old, green wild-type and dgt plants were also equally sensitive to cytokinin with respect to shoot growth and hypocotyl and internode elongation. The effects of cytokinin and the dgt mutation on these processes appeared additive. In tissue culture organ regeneration from dgt hypocotyl explants showed reduced sensitivity to auxin but normal sensitivity to cytokinin, and the effects of cytokinin and the mutation were again additive. However, although callus induction from dgt hypocotyl explants required auxin and cytokinin, dgt calli did not show the typical concentration-dependent stimulation of growth by either auxin or cytokinin observed in wild-type cells. Cross-resistance of the dgt mutant to cytokinin thus was found to be limited to a small subset of auxin- and cytokinin-regulated growth processes affected by the dgt mutation, indicating that auxin and cytokinin regulate plant growth through both shared and separate signaling pathways.

Isolation and expression pattern of hahr1, a homeobox-containing cDNA from Helianthus annuus

A 2.5 kb homeobox (HB)-containing cDNA (hahr1) was isolated from a library prepared from rootlets of Helianthus annuus using a polymerase chain reaction (PCR)-based strategy. The putative protein product (77 kDa) contains the homeodomain (HD) and an acidic domain at the N-terminal region (residues 72-155). The deduced amino acid sequence of hahr1 shares a 53% sequence identity with GLABRA2, a HD protein associated with epidermal cell differentiation. Hahr1 expression was primarily found in dry seeds, hypocotyls and roots at stages associated with early developmental events. Expression was completely lacking in leaves and flowers. Evidence for the existence of one related gene expressed in sunflower stems was obtained by the presence of restriction fragment length polymorphism of amplified cDNA products.

The petunia homologue of tomato gast1: transcript accumulation coincides with gibberellin-induced corolla cell elongation

Gibberellins (GAs) regulate petunia corolla pigmentation and elongation. To study this hormone's effect at the molecular level, we used the tomato gast1 gene as a probe to isolate a gibberellin-induced gene (gip) from petunia corollas. The deduced sequence of gip exhibited 82% identity with GAST1 protein and contained a short, highly hydrophobic N-terminal region. High levels of gip expression were detected in elongating corollas and young stem intemodes. When detached corollas were grown in vitro in sucrose medium, gip expression was strongly induced by gibberellic acid (GA3). GA3-induced gip expression in corollas was inhibited by abscisic acid (ABA). The expression of the gene was also induced by GA3 in detached young stem segments. Sucrose was not essential for GA-induced gip expression in corollas but enhanced its effect. In stems, on the other hand, sucrose inhibited the effect of the hormone. The results of the present work support the possible role of gip in GA-induced corolla and stem elongation.

Isolation of a root-specific cDNA encoding a ns-LTP-like protein from the roots of bean (Phaseolus vulgaris L.) seedlings

A root-specific cDNA clone, PVR3, was isolated from a bean (Phaseolus vulgaris L.) root cDNA library by a differential screening procedure. The nucleotide sequence of PVR3 contains an open reading frame coding for an 11.14 kDa polypeptide of 102 amino acid residues; the first 25 amino acids correspond to the sequence characteristic of a signal peptide. Comparison of the deduced PVR3 polypeptide sequence with the polypeptide sequences of previously cloned genes indicates that PVR3 may encode a ns-LTP-like protein. Molecular modelling of the PVR3 protein predicts that it has a three-dimensional structure that is similar to the three-dimensional model determined from the maize ns-LTP. The PVR3 mRNA accumulated mainly in the roots of young seedlings. It can be detected at low levels in flowers, but it is not detected in other organs. Genomic Southern blot analysis indicates that the genomic DNA corresponding to PVR3 cDNA is encoded by a single gene or small gene family in the bean genome.

Characterization of a cDNA encoding a proline-rich 14 kDa protein in developing cortical cells of the roots of bean (Phaseolus vulgaris) seedlings

A cDNA clone, corresponding to mRNAs preferentially expressed in the roots of bean (Phaseolus vulgaris L.) seedlings, was isolated. This clone contains a 381 bp open reading frame encoding a polypeptide of 13.5 kDa, designated PVR5 (Phaseolus vulgaris root 5). The amino acid sequence of this clone is rich in proline (13.5%) and leucine (12.7%) and shares significant amino acid sequence homology with root-specific and proline-rich proteins from monocots (maize and rice), and proline-rich proteins from dicots (carrot, oilseed rape, and Madagascar periwinkle). The precise biological roles of these polypeptides are unknown. PVR5 mRNA accumulation is developmentally regulated within the root, with high levels at the root apex and declining levels at distances further from the root tip. In situ hybridization shows that PVR5 mRNA specifically accumulates in the cortical ground meristem in which maximal cell division occurs. Southern blot analysis suggests that genomic DNA corresponding to PVR5 cDNA is encoded by a single gene or a small gene family.

Phaseolus ENOD40 is involved in symbiotic and non-symbiotic organogenetic processes: expression during nodule and lateral root development

ENOD40 is an early nodulin gene, recently isolated from legume species forming nodules either after Rhizobium infection or spontaneously. ENOD40 cDNAs from Phaseolus plants were isolated and nucleotide sequence determination revealed 85% and 88.5% homology with the reported soybean cDNA clones. The putative polypeptide deduced coincides with the soybean one but a stop codon, almost in the middle of the respective ORF, renders it much shorter. This polypeptide was overexpressed as a fusion protein in Escherichia coli. Although the spatial expression pattern of the gene in the root pericycle and nodule primordium at early stages of development as well as in the pericycle of the vascular bundles and uninfected cells in mature nodules is comparable to the gene's expression pattern in soybean, differences in developmental regulation are evident. We have shown that ENOD40 transcripts are also detected at very early stages of lateral root development, in the dividing pericycle cells of the root stele that give rise to the lateral root primordia. The presence of Rhizobium causes an enhancement of the gene's expression and also induction of the gene in the vascular tissues of developed lateral roots. Interestingly, a discrimination on the gene's expression level in adventious and acropetal incipient lateral root primordia, emerging in infected and uninfected roots, is observed. This indicates that the gene's product may be involved in the hormonal status of the plant and that ENOD40 may be used as a molecular marker in lateral root initiation.