A TM3-like MADS-box gene from Eucalyptus expressed in both vegetative and reproductive tissues

Molecular cloning and potential function prediction of homologous SOC1 genes in tree peony

KEY MESSAGE

The central flower integrator PsSOC1 was isolated and its expression profiles were analyzed; then the potential function of PsSOC1 in tree peony was postulated. The six flowering genes PrSOC1, PdSOC1, PsSOC1, PsSOC1-1, PsSOC1-2, and PsSOC1-3 were isolated from Paeonia rockii, Paeonia delavayi, and Paeonia suffruticosa, respectively. Sequence comparison analysis showed that the six genes were highly conserved and shared 99.41% nucleotide identity. Further investigation suggested PsSOC1 was highly homologous to the floral integrators, SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), from Arabidopsis. Phylogenetic analysis showed that the SOC1 protein clustering has family specificity and PsSOC1 has a close relationship with homologous SOC1 from Asteraceae species. The studies of PsSOC1's expression patterns in different buds and flower buds, and vegetative organs indicated that PsSOC1 could express in both vegetative and reproductive organs. While the expression of PsSOC1 in different developmental stages of buds was different; high expression levels of PsSOC1 occurred in the bud at the bud sprouting stage and the type I aborted the flower bud. PsSOC1 expression was also shown to be affected by gibberellins (GA), low temperature, and photoperiod. One of the pathways that regulates tree peony flowering may be the GA-inductive pathway. Ectopic expression of PsSOC1 in tobacco demonstrated that greater PsSOC1 expression in the transgenic tobacco plants not only promoted plant growth, but also advanced the flowering time. Finally, the potential function of PsSOC1 in tree peony was postulated.

Functional and expression analyses of kiwifruit SOC1-like genes suggest that they may not have a role in the transition to flowering but may affect the duration of dormancy

The MADS-domain transcription factor SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) is one of the key integrators of endogenous and environmental signals that promote flowering in the annual species Arabidopsis thaliana. In the deciduous woody perennial vine kiwifruit (Actinidia spp.), environmental signals are integrated to regulate annual cycles of growth and dormancy. Accumulation of chilling during winter is required for dormancy break and flowering in spring. In order to understand the regulation of dormancy and flowering in kiwifruit, nine kiwifruit SOC1-like genes were identified and characterized. All genes affected flowering time of A. thaliana Col-0 and were able to rescue the late flowering phenotype of the soc1-2 mutant when ectopically expressed. A differential capacity for homodimerization was observed, but all proteins were capable of strong interactions with SHORT VEGETATIVE PHASE (SVP) MADS-domain proteins. Largely overlapping spatial domains but distinct expression profiles in buds were identified between the SOC1-like gene family members. Ectopic expression of AcSOC1e, AcSOC1i, and AcSOC1f in Actinidia chinensis had no impact on establishment of winter dormancy and failed to induce precocious flowering, but AcSOC1i reduced the duration of dormancy in the absence of winter chilling. These findings add to our understanding of the SOC1-like gene family and the potential diversification of SOC1 function in woody perennials.

Cloning and functional analysis of the flowering gene GmSOC1-like, a putative SUPPRESSOR OF OVEREXPRESSION CO1/AGAMOUS-LIKE 20 (SOC1/AGL20) ortholog in soybean

KEY MESSAGE

The major insight in this manuscript is that we identified a new flowering regulator, GmSOC1-like, which may participate in the initiation and maintenance of flowering in soybean. Flowering is pivotal for the reproductive behavior of plants, and it is regulated by complex and coordinated genetic networks that are fine-tuned by endogenous cues and environmental signals. To better understand the molecular basis of flowering regulation in soybean, we isolated GmSOC1 and GmSOC1-like, two putative soybean orthologs for the Arabidopsis SUPPRESSOR OF OVEREXPRESSION OF CO1/AGAMOUS-LIKE 20 (SOC1/AGL20). The expression pattern of GmSOC1-like was analyzed by qRT-PCR in Zigongdongdou, a photoperiod-sensitive soybean cultivar. GmSOC1-like was widely expressed at different levels in most organs of the soybean, with the highest expression in the shoot apex during the early stage of floral transition. In addition, its expression showed a circadian rhythm pattern, with the highest expression at midnight under short-day (SD) condition. Intriguingly, GmSOC1-like was induced 4 days earlier than GmSOC1 during flowering transition in SD, suggesting that GmSOC1 and GmSOC1-like expression might be differentially regulated. However, under long-day (LD) condition, the expression of GmSOC1 and GmSOC1-like decreased gradually in the shoot apex of Zigongdongdou, which is in accordance with the fact that Zigongdongdou maintains vegetative growth in LD. In addition, overexpression of GmSOC1-like stimulated the flowering of Lotus corniculatus cv. supperroot plants. In conclusion, the results of this study indicate that GmSOC1-like may act as a flowering inducer in soybean.

Cloning and expression analysis of GmGAL1, SOC1 homolog gene in soybean

A MADS box gene AGL20/SOC1 is a main integrator in Arabidopsis flowering pathway whose structure and function are highly conserved in many plant species. A soybean MADS box gene GmGAL1 (Glycine max AGAMOUS Like 1) as a homolog of AGL20/SOC1, was cloned from soybean cultivar Kennong18 and its function was investigated in transgenic Arabidopsis lines. Sequence comparisons showed that the closest homolog gene to GmGAL1 is AGL20/SOC1 in Arabidopsis and VuSOC1 in Vigna unguiculata. We investigated the expression level of GmGAL1 using quantitative real-time PCR, and the result showed that GmGAL1 was regulated by a circadian mechanism and its expression oscillated at a cycle of 24 h. The expression level of GmGAL1 was fluctuated in diverse tissues/organs and developmental stages. Considering its expression can be detected in different tissues throughout the life cycle and its protein localized in cytoplasm in Arabidopsis protoplasm, we proposed that GmGAL1 may be a multifunctional gene in the context of the soybean development. Ectopic expression of GmGAL1 in Arabidopsis enhanced flowering under long-day condition and partially rescued soc1 late flowering type.

Over-expression of the Gerbera hybrida At-SOC1-like1 gene Gh-SOC1 leads to floral organ identity deterioration

BACKGROUND AND AIMS

The family of MADS box genes is involved in a number of processes besides controlling floral development. In addition to supplying homeotic functions defined by the ABC model, they influence flowering time and transformation of vegetative meristem into inflorescence meristem, and have functions in roots and leaves. Three Gerbera hybrida At-SOC1-like genes (Gh-SOC1-Gh-SOC3) were identified among gerbera expressed sequence tags.

METHODS

Evolutionary relationships between SOC1-like genes from gerbera and other plants were studied by phylogenetic analysis. The function of the gerbera gene Gh-SOC1 in gerbera floral development was studied using expression analysis, protein-protein interaction assays and reverse genetics. Transgenic gerbera lines over-expressing or downregulated for Gh-SOC1 were obtained using Agrobacterium transformation and investigated for their floral phenotype.

KEY RESULTS

Phylogenetic analysis revealed that the closest paralogues of At-SOC1 are Gh-SOC2 and Gh-SOC3. Gh-SOC1 is a more distantly related paralogue, grouping together with a number of other At-SOC1 paralogues from arabidopsis and other plant species. Gh-SOC1 is inflorescence abundant and no expression was seen in vegetative parts of the plant. Ectopic expression of Gh-SOC1 did not promote flowering, but disturbed the development of floral organs. The epidermal cells of ray flower petals appeared shorter and their shape was altered. The colour of ray flower petals differed from that of the wild-type petals by being darker red on the adaxial side and greenish on the abaxial surface. Several protein-protein interactions with other gerbera MADS domain proteins were identified.

CONCLUSIONS

The At-SOC1 paralogue in gerbera shows a floral abundant expression pattern. A late petal expression might indicate a role in the final stages of flower development. Over-expression of Gh-SOC1 led to partial loss of floral identity, but did not affect flowering time. Lines where Gh-SOC1 was downregulated did not show a phenotype. Several gerbera MADS domain proteins interacted with Gh-SOC1.

Identification of PTM5 protein interaction partners, a MADS-box gene involved in aspen tree vegetative development

In a past article, our lab described the identification and characterization of a novel vegetative MADS-box gene from quaking aspen trees, Populus tremuloides MADS-box 5 (PTM5). PTM5 was shown to be a member of the SOC1/TM3 class of MADS-box genes with a seasonal expression pattern specific to developing vascular tissues including the vascular cambium, the precursor to all woody branches, stems, and roots. Since the proper function of MADS-box proteins is dependent on specific interactions with other regulatory proteins, we further examined PTM5 protein-protein interactions as a means to better understand its function. Through yeast two-hybrid analyses, it was demonstrated that, like other SOC1/TM3 class proteins, PTM5 is capable of interacting with itself as well as other MADS-box proteins from aspen. In addition, yeast two-hybrid library screening revealed that PTM5 interacts with two non-MADS proteins, an actin depolymerizing factor (PtADF) and a novel leucine-rich repeat protein (PtLRR). In situ RNA localization was used to verify the overlapping expression patterns of these genes, and transgenic studies showed that over-expression of PTM5 in aspen causes alterations in root vasculature and root biomass development consistent with the cell growth and expansion functions of related ADF and LRR genes. These results suggest that the interaction of vegetative MADS-box genes with specific protein cofactors is a key step in the mechanisms that control woody tissue development in trees.

Genomic research in Eucalyptus

Eucalyptus L'Hérit. is a genus comprised of more than 700 species that is of vital importance ecologically to Australia and to the forestry industry world-wide, being grown in plantations for the production of solid wood products as well as pulp for paper. With the sequencing of the genomes of Arabidopsis thaliana and Oryza sativa and the recent completion of the first tree genome sequence, Populus trichocarpa, attention has turned to the current status of genomic research in Eucalyptus. For several eucalypt species, large segregating families have been established, high-resolution genetic maps constructed and large EST databases generated. Collaborative efforts have been initiated for the integration of diverse genomic projects and will provide the framework for future research including exploiting the sequence of the entire eucalypt genome which is currently being sequenced. This review summarises the current position of genomic research in Eucalyptus and discusses the direction of future research.

Characterization of TrcMADS1 gene of Trillium camtschatcense (Trilliaceae) reveals functional evolution of the SOC1/TM3-like gene family

Plant MADS-box genes encode transcriptional regulators that are critical for a number of developmental processes, such as the establishment of floral organ identity, flowering time, and fruit development. It appears that the MADS-box gene family has undergone considerable gene duplication and divergence within various angiosperm lineages. SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1)/Tomato MADS-box gene 3 (TM3)-like genes are members of the MADS-box gene family and have undergone repeated duplication events. Here, we isolated and characterized the SOC1/TM3-like gene TrcMADS1 from Trillium camtschatcense (Trilliaceae) to infer the ancestral function of SOC1/TM3-like genes. The alignment of SOC1/TM3-like genes revealed the presence of a highly conserved region in the C-terminal of predicted protein sequences, designated the SOC1 motif. Phylogenetic analysis indicated that TrcMADS1 is at the basal position of the SOC1/TM3-like gene family. The TrcMADS1 mRNA was detected in both vegetative and reproductive organs by RT-PCR. Our results suggest that duplicated copies of SOC1/TM3-like gene evolved to become variously functionally specialized.

Characterization of PTM5 in aspen trees: a MADS-box gene expressed during woody vascular development

The vascular component of trees possesses some of the most specialized processes active in the formation of roots, stems, and branches, and its wood component continues to be of primary importance to our daily lives. The molecular mechanisms of wood development, however, remain poorly understood with few well-characterized regulatory genes. We have identified a vascular tissue-specific MADS-box gene, Populus tremuloides MADS-box 5 (PTM5) that is expressed in differentiating primary and secondary xylem and phloem. Phylogenetic analysis has shown that PTM5 is a member of the SOC1/TM3 class of MADS-box genes. Temporal expression analysis of PTM5 in staged vascular cambium and other tissues indicated that PTM5 expression is seasonal and is limited to spring wood formation and rapidly expanding floral catkins. Spatial expression analysis using in situ hybridization revealed that PTM5 expression is localized within a few layers of differentiating vascular cambium and xylem tissues as well as the vascular bundles of expanding catkins. Since many MADS-box genes are known to act as transcription factors, these results suggest that the coordinated expression of PTM5 with other vascular developmental genes may be a hallmark of the complex events that lead to the formation of the woody plant body.

MADS-box gene evolution-structure and transcription patterns

This study presents a phylogenetic analysis of 198 MADS-box genes based on 420 parsimony-informative characters. The analysis includes only MIKC genes; therefore several genes from gymnosperms and pteridophytes are excluded. The strict consensus tree identifies all major monophyletic groups known from earlier analyses, and all major monophyletic groups are further supported by a common gene structure in exons 1-6 and by conserved C-terminal motifs. Transcription patterns are mapped on the tree to obtain an overview of MIKC gene transcription. Genes that are transcribed only in vegetative organs are located in the basal part of the tree, whereas genes involved in flower development have evolved later. As the universality of the ABC model has recently been questioned, special account is paid to the expression of A-, B-, and C-class genes. Mapping of transcription patterns on the phylogeny shows all three classes of MADS-box genes to be transcribed in the stamens and carpels. Thus the analysis does not support the ABC model as formulated at present.