Isolation and expression analysis of a tobacco AINTEGUMENTA ortholog (NtANTL)

Two FD homologs from London plane (Platanus acerifolia) are associated with floral initiation and flower morphology

The flowering-time gene FD encodes a bZIP transcription factor that interacts with FLOWERING LOCUS T (FT) to induce flowering in Arabidopsis. Previous research has identified two FT homologs of Platanus acerifolia, PaFT and PaFTL, which each have different expression patterns and are involved in diverse developmental processes. However, it is not known whether such FT/FD complexes participate in the flowering processes in P. acerifolia. Therefore, we isolated two closely related FD homologs, PaFDL1 and PaFDL2, and investigated their functions through the analysis of expression profiles, transgenic phenotypes, their interactions with different FT proteins, and potential cis-regulatory elements in their promoters. The PaFDL genes were found to display their maximal expression levels during the stage of floral transition, and subsequent expression patterns were also seen to be related to inflorescence developmental stage. In addition, both PaFDL1 and PaFDL2 were found to be subject to post-transcriptional alternative splicing, each gene producing two transcript forms. Transgenic tobacco overexpressing each of the four resulting transcript types displayed accelerated floral initiation and produced abnormal flowers. The results suggested that the complete PaFDL proteins may interact with different PaFT/PaFTL proteins in order to fulfill both conservative and diverse functions in floral initiation and floral development.

Expression profiles and hormonal regulation of tobacco NtEXGT gene and its involvement in abiotic stress response

Despite the intensive study of xyloglucan endotransglucosylases/hydrolases, their multifaceted role in plant growth regulation in changing environmental conditions is not yet clarified. The functional role of the large number of genes encoding this group of enzymes is also still unclear. NtEXGT gene encodes one of xyloglucan endotransglucosylases/hydrolases (XTHs) of Nicotiana tabacum L. The highest level of NtEXGT gene expression was detected in young flowers and leaves near the shoot apex. Expression of the NtEXGT gene in leaves was induced by cytokinins, auxins, brassinosteroids and gibberellins. NtEXGT gene was also up-regulated by salinity, drought, cold, cadmium and 10 μM abscisic acid treatments and down-regulated in response to 0 °C and 100 μM abscisic acid. Pretreatment of leaves with fluridone contributed to smaller increase in the level of NtEXGT transcripts in response to drought stress. These data suggest that NtEXGT gene is ABA-regulated and probably implicated in ABA-dependent signaling in response to stress factors. 35S::NtEXGT plants of tobacco showed higher rate of root growth under salt-stress conditions, greater frost and heat tolerance as compared with the wild type tobacco plants.

Transcriptome Analysis of Soybean Leaf Abscission Identifies Transcriptional Regulators of Organ Polarity and Cell Fate

Abscission, organ separation, is a developmental process that is modulated by endogenous and environmental factors. To better understand the molecular events underlying the progression of abscission in soybean, an agriculturally important legume, we performed RNA sequencing (RNA-seq) of RNA isolated from the leaf abscission zones (LAZ) and petioles (Non-AZ, NAZ) after treating stem/petiole explants with ethylene for 0, 12, 24, 48, and 72 h. As expected, expression of several families of cell wall modifying enzymes and many pathogenesis-related (PR) genes specifically increased in the LAZ as abscission progressed. Here, we focus on the 5,206 soybean genes we identified as encoding transcription factors (TFs). Of the 5,206 TFs, 1,088 were differentially up- or down-regulated more than eight-fold in the LAZ over time, and, within this group, 188 of the TFs were differentially regulated more than eight-fold in the LAZ relative to the NAZ. These 188 abscission-specific TFs include several TFs containing domains for homeobox, MYB, Zinc finger, bHLH, AP2, NAC, WRKY, YABBY, and auxin-related motifs. To discover the connectivity among the TFs and highlight developmental processes that support organ separation, the 188 abscission-specific TFs were then clustered based on a >four-fold up- or down-regulation in two consecutive time points (i.e., 0 and 12 h, 12 and 24 h, 24 and 48 h, or 48 and 72 h). By requiring a sustained change in expression over two consecutive time intervals and not just one or several time intervals, we could better tie changes in TFs to a particular process or phase of abscission. The greatest number of TFs clustered into the 0 and 12 h group. Transcriptional network analysis for these abscission-specific TFs indicated that most of these TFs are known as key determinants in the maintenance of organ polarity, lateral organ growth, and cell fate. The abscission-specific expression of these TFs prior to the onset of abscission and their functional properties as defined by studies in Arabidopsis indicate that these TFs are involved in defining the separation cells and initiation of separation within the AZ by balancing organ polarity, roles of plant hormones, and cell differentiation.

Role of AINTEGUMENTA-like gene NtANTL in the regulation of tobacco organ growth

The Nicotiana tabacum AINTEGUMENTA-like gene (NtANTL), encoding one of AP2/ERF transcription factors, is a putative ortholog of the AtANT gene from Arabidopsis thaliana. In wild-type tobacco plants, the NtANTL gene was expressed in the actively dividing young flowers, shoot apices, and calluses, while the level of its mRNA increased considerably after treatment with exogenous 6-benzylaminopurine, indoleacetic acid and 24-epibrassinolide. We found a positive correlation among the expression levels of NtANTL, cyclin NtCYCD3;1 and cyclin-dependent kinase NtCDKB1-1 genes, suggesting possible molecular links between AINTEGUMENTA and cell cycle regulators in tobacco plants. However, no correlation was observed between NtANTL, NtCYCD3;1 and NtCDKB1-1 expression levels in response to NaCl and ABA. These observations indicate that the transcription factor NtANTL was not involved in the regulation of the cellular response to salinity nor did it affect the expression of NtCYCD3;1 and NtCDKB1-1 when tobacco plants were exposed to salt stress and ABA. In addition, we generated transgenic tobacco plants with both up-regulated and down-regulated expression of the NtANTL gene. Constitutive expression of the NtANTL gene contributed to an increase in the size of leaves and corolla of transgenic plants. Transgenic plants with reduced expression of the NtANTL gene had smaller leaves, flowers and stems, but showed a compensatory increase in the cell size of leaves and flowers. The results show the significance of the NtANTL gene for the control of organ growth by both cell division and expansion in tobacco plants.

Validation of Aintegumenta as a gene to modify floral size in ornamental plants

The gene AINTEGUMENTA (AtANT) is an APETALA2 transcription factor in Arabidopsis activating growth downstream of auxin signalling. Lateral organ size is positively correlated with ANT expression in Arabidopsis. We tested the use of AtANT as a tool to modify floral size in two different plants used as model organisms and ornamental crops, Petunia × hybrida and Antirrhinum majus. Petunia plants expressing PhANT RNAi showed a decrease in PhANT expression correlated with smaller petal limbs. In contrast Petunia plants overexpressing AtANT had larger petal limbs. Petal tube length was less affected in down-regulation of PhANT or overexpression of AtANT. Overexpression of AtANT in Antirrhinum caused increased flower size via increased petal limb width and tube length. Down-regulation of PhANT showed an effect on cell size while overexpression of AtANT in Petunia and Antirrhinum caused significant increases in cell expansion that could explain the differences in floral organ size. The endogenous expression levels of PhANT and AmANT tended to be higher in the limb than in the tube in both Antirrhinum and Petunia. AtANT overexpression caused significant AmANT up-regulation in Antirrhinum limbs but not of PhANT in Petunia, indicating differences in the regulatory network. The differential effect of AtANT on limb and tube in Petunia and Antirrhinum correspond to phenotypic differences observed in natural variation in the corresponding genus indicating a relation between the phenotypic space of a genus and the effect of modified ANT levels, validating ANT as a gene to modify floral size.

AINTEGUMENTA-LIKE proteins: hubs in a plethora of networks

Members of the AINTEGUMENTA-LIKE (AIL) family of APETALA 2/ETHYLENE RESPONSE FACTOR (AP2/ERF) domain transcription factors are expressed in all dividing tissues in the plant, where they have central roles in developmental processes such as embryogenesis, stem cell niche specification, meristem maintenance, organ positioning, and growth. When overexpressed, AIL proteins induce adventitious growth, including somatic embryogenesis and ectopic organ formation. The Arabidopsis (Arabidopsis thaliana) genome contains eight AIL genes, including AINTEGUMENTA, BABY BOOM, and the PLETHORA genes. Studies on these transcription factors have revealed their intricate relationship with auxin as well as their involvement in an increasing number of gene regulatory networks, in which extensive crosstalk and feedback loops have a major role.

Arabidopsis ovule development and its evolutionary conservation

Ovules have an important role during the life cycle of the plant, and they provide an excellent model for studying organogenesis in plants. As such, the molecular control of ovule development has been studied for many years. Recent studies in Arabidopsis have revealed important new data concerning ovule primordia formation, ovule identity determination, and patterning. Furthermore, interesting results about ovule development in other species, such as Petunia and rice, have been published recently. In this review, we discuss these recent findings in reference to ovule development in Arabidopsis. We compare available data with those of other species to investigate the evolutionary conservation of the regulatory pathways.

Mapping sequences required for nuclear localization and the transcriptional activation function of the Arabidopsis protein AINTEGUMENTA

The Arabidopsis thaliana floral development protein AINTEGUMENTA (ANT) is a member of a large family of DNA binding proteins (AP2/ERF family) that control plant growth and development in response to developmental or environmental signals. Transcriptional activation and/or repression activities have been demonstrated for several members of this protein family. We have used fusions between ANT and the GAL4 DNA binding domain to identify an 80 amino acid sequence important for the transcriptional activation function of ANT. This region shows similarity to transcriptional activation domains in other proteins, as it is rich in Ser/Thr, Gln/Asn, and acidic amino acids. We also demonstrate that ANT can activate gene expression in Arabidopsis plants through binding to a DNA sequence corresponding to an in vitro determined ANT binding site. Finally, we show that ANT is nuclear localized and that the sequence KKKR (amino acids 252-255) is required for nuclear localization of the protein.