Quantitative expression analysis of the ABC genes in Sophora tetraptera, a woody legume with an unusual sequence of floral organ development

Phase change and flowering in woody plants of the New Zealand flora

Heteroblastic and homoblastic woody plants from the New Zealand flora provide a rich playground for testing hypotheses relating to phase change and flowering.

Comparative transcriptome analysis of the floral transition in Rosa chinensis 'Old Blush' and R. odorata var. gigantea

The floral transition is a crucial developmental event, but little is known about the underlying regulatory networks in seasonally and continuously flowering roses. In this study, we compared the genetic basis of flowering in two rose species, Rosa chinensis ‘Old Blush’, which flowers continuously, and R. odorata var. gigantea, which blooms in early spring. Gene ontology (GO) terms related to methylation, light reaction, and starch metabolism were enriched in R. odorata var. gigantea and terms associated with sugar metabolism were enriched in R. chinensis ‘Old Blush’ during the floral transition. A MapMan analysis revealed that genes involved in hormone signaling mediate the floral transition in both taxa. Furthermore, differentially expressed genes (DEGs) involved in vernalization, photoperiod, gibberellin (GA), and starch metabolism pathways converged on integrators, e.g., LFY, AGL24, SOC1, CAL, and COLs, to regulate the floral transition in R. odorata var. gigantea, while DEGs related to photoperiod, sugar metabolism, and GA pathways, including COL16, LFY, AGL11, 6PGDH, GASA4, and BAM, modulated the floral transition in R. chinensis ‘Old Blush.’ Our analysis of the genes underlying the floral transition in roses with different patterns of flowering provides a basis for further functional studies.

Generation and Characterisation of a Reference Transcriptome for Lentil (Lens culinaris Medik.)

RNA-Seq using second-generation sequencing technologies permits generation of a reference unigene set for a given species, in the absence of a well-annotated genome sequence, supporting functional genomics studies, gene characterisation and detailed expression analysis for specific morphophysiological or environmental stress response traits. A reference unigene set for lentil has been developed, consisting of 58,986 contigs and scaffolds with an N50 length of 1719 bp. Comparison to gene complements from related species, reference protein databases, previously published lentil transcriptomes and a draft genome sequence validated the current dataset in terms of degree of completeness and utility. A large proportion (98%) of unigenes were expressed in more than one tissue, at varying levels. Candidate genes associated with mechanisms of tolerance to both boron toxicity and time of flowering were identified, which can eventually be used for the development of gene-based markers. This study has provided a comprehensive, assembled and annotated reference gene set for lentil that can be used for multiple applications, permitting identification of genes for pathway-specific expression analysis, genetic modification approaches, development of resources for genotypic analysis, and assistance in the annotation of a future lentil genome sequence.

Morphology and quantitative monitoring of gene expression patterns during floral induction and early flower development in Dendrocalamus latiflorus

The mechanism of floral transition in bamboo remains unclear. Dendrocalamus latiflorus (Bambusease, Bambusoideae, Poaceae) is an economically and ecologically important clumping bamboo in tropical and subtropical areas. We evaluated morphological characteristics and gene expression profiling to study floral induction and early flower development in D. latiflorus. The detailed morphological studies on vegetative buds and floral organography were completed using paraffin sectioning and scanning electron microscopy. The 3 mm floral buds commence the development of stamen primordia and pistil primordium. Furthermore, homologs of floral transition-related genes, including AP1, TFL1, RFL, PpMADS1, PpMADS2, SPL9, FT, ID1, FCA, and EMF2, were detected and quantified by reverse transcriptase PCR and real-time PCR in vegetative and floral buds, respectively. Distinct expression profiles of ten putative floral initiation homologues that corresponded to the developmental stages defined by bud length were obtained and genes were characterized. Six of the genes (including DlTFL1, DlRFL, DlMADS2, DlID1, DlFCA, DlEMF2) showed statistically significant changes in expression during floral transition. DlAP1 demonstrated a sustained downward trend and could serve as a good molecular marker during floral transition in D. latiflorus. The combined analysis provided key candidate markers to track the transition from the vegetative to reproductive phase.

The corona of the daffodil Narcissus bulbocodium shares stamen-like identity and is distinct from the orthodox floral whorls

The structural homology of the daffodil corona has remained a source of debate throughout the history of botany. Over the years it has been separately referred to as a modified petal stipule, stamen and tepal. Here we provide insights from anatomy and molecular studies to clarify the early developmental stages and position of corona initiation in Narcissus bulbocodium. We demonstrate that the corona initiates as six separate anlagen from hypanthial tissue between the stamens and perianth. Scanning electron microscope images and serial sections demonstrate that corona initiation occurs late in development, after the other floral whorls are fully developed. To define more precisely the identity of the floral structures, daffodil orthologues of the ABC floral organ identity genes were isolated and expression patterns were examined in perianth, stamens, carpel, hypanthial tube and corona tissue. Coupled with in situ hybridisation experiments, these analyses showed that the expression pattern of the C-class gene NbAGAMOUS in the corona is more similar to that of the stamens than that of the tepals. In combination, our results demonstrate that the corona of the daffodil N. bulbocodium exhibits stamen-like identity, develops independently from the orthodox floral whorls and is best interpreted as a late elaboration of the region between the petals and stamens associated with epigyny and the hypanthium.

Co-ordinate regulation of cytokinin gene family members during flag leaf and reproductive development in wheat

BACKGROUND

As the global population continues to expand, increasing yield in bread wheat is of critical importance as 20% of the world's food supply is sourced from this cereal. Several recent studies of the molecular basis of grain yield indicate that the cytokinins are a key factor in determining grain yield. In this study, cytokinin gene family members in bread wheat were isolated from four multigene families which regulate cytokinin synthesis and metabolism, the isopentenyl transferases (IPT), cytokinin oxidases (CKX), zeatin O-glucosyltransferases (ZOG), and β-glucosidases (GLU). As bread wheat is hexaploid, each gene family is also likely to be represented on the A, B and D genomes. By using a novel strategy of qRT-PCR with locus-specific primers shared among the three homoeologues of each family member, detailed expression profiles are provided of family members of these multigene families expressed during leaf, spike and seed development.

RESULTS

The expression patterns of individual members of the IPT, CKX, ZOG, and GLU multigene families in wheat are shown to be tissue- and developmentally-specific. For instance, TaIPT2 and TaCKX1 were the most highly expressed family members during early seed development, with relative expression levels of up to 90- and 900-fold higher, respectively, than those in the lowest expressed samples. The expression of two cis-ZOG genes was sharply increased in older leaves, while an extremely high mRNA level of TaGLU1-1 was detected in young leaves.

CONCLUSIONS

Key genes with tissue- and developmentally-specific expression have been identified which would be prime targets for genetic manipulation towards yield improvement in bread wheat breeding programmes, utilising TILLING and MAS strategies.

Expression of floral identity genes in Clianthus maximus during mass inflorescence abortion and floral development

BACKGROUND AND AIMS

Clianthus maximus is a leguminous perennial with an unusual order of floral organ insertion, and inflorescences produced year round that nearly all abort except during a limited time in autumn. This study aimed to determine at what point in floral organ differentiation abortion occurred and whether the expression of the floral identity genes underlies this cessation in flower development.

METHODS

Inflorescences were harvested across an annual cycle and flower development was examined by light and scanning electron microscopy. Expression of the C. maximus-equivalents of LEAFY (LFY), APETALA1 (AP1), PISTILLATA (PI) and AGAMOUS (AG) was monitored simultaneously by quantitative, reverse transcriptase PCR.

KEY RESULTS

Only those inflorescences formed in autumn proceeded to anthesis. Organogenesis had not begun in inflorescences that aborted. The C. maximus-equivalents of AP1, PI and AG were expressed in sepals, petals, carpels and stamens, as expected from the ABC model of floral organ identity specification; furthermore, the order of expression of the three genes reflected the unusual pattern of organ differentiation. Low expression of LFY and AP1 was observed during inflorescence abortion.

CONCLUSIONS

Predictions of gene expression based on the ABC model were upheld despite the unusual mass abortion of inflorescences and the non-standard pattern of organ formation. The lack of expression of LFY and AP1 in inflorescences may have been the cause of inflorescence abortion.

MADS: the missing link between identity and growth?

Size and shape are intrinsic characteristics of any given plant organ and, therefore, are inherently connected with its identity. How the connection between identity and growth is established at the molecular level remains one of the key questions in developmental biology. The identity of floral organs is determined by a hierarchical combination of transcription factors, most of which belong to the MADS box family. Recent progress in finding the target genes of these master regulators reopened the debate about the missing link between identity and floral organ growth. Here, we review these novel findings and integrate them into a model, to show how MADS proteins, in concert with co-factors, could fulfill their role at later stages of floral organ development when size and shape are established.

Quantitative expression analysis of meristem identity genes in Eucalyptus occidentalis: AP1 is an expression marker for flowering

A number of Eucalyptus species exhibit precocious flowering, flowering within a year of germination and often while still exhibiting juvenile foliage. To understand the nature of precocious flowering in Eucalyptus occidentalis, partial homologues of the inflorescence meristem identity gene TERMINAL FLOWER1 and of the floral meristem identity genes LEAFY and APETALA1 (EOTFL1, EOLFY and EOAP1, respectively) were isolated and characterized. The expression patterns of these meristem identity genes during the development of branched and single-stem plants were analysed by quantitative reverse transcriptase PCR. All E. occidentalis plants commenced flowering within 40 weeks of germination. However, the branched plants reached maximum flowering some 5-6 weeks earlier than did single-stem plants. Levels of EOTFL1 and EOLFY expression varied little during the study period irrespective of architecture treatment, whereas expression of EOAP1 reached a peak coincident with peak flowering in both branched and single-stem plants. AP1 is clearly an expression marker for flowering in this species.