The role of miR156 in developmental transitions in Nicotiana tabacum

Plants undergo a series of developmental transitions during their life cycle. After seed germination, plants pass through two distinct phases: the vegetative phase in which leaves are produced and the reproductive phase in which flowering occurs. Based on the reproductive competence and morphological changes, the vegetative phase can be further divided into juvenile and adult phases. Here, we demonstrate that the difference between juvenile and adult phase of Nicotiana tabacum is characterized by the changes in leaf size, leaf shape as well as the number of leaf epidermal hairs(trichomes). We further show that miR156, an age-regulated microR NA, regulates juvenile-to-adult phase transition in N. tabacum. Overexpression of miR156 results in delayed juvenile-to-adult transition and flowering. Together, our results support an evolutionarily conserved role of miR156 in plant developmental transitions.     

miRNA control of vegetative phase change in trees

After germination, plants enter juvenile vegetative phase and then transition to an adult vegetative phase before producing reproductive structures. The character and timing of the juvenile-to-adult transition vary widely between species. In annual plants, this transition occurs soon after germination and usually involves relatively minor morphological changes, whereas in trees and other perennial woody plants it occurs after months or years and can involve major changes in shoot architecture. Whether this transition is controlled by the same mechanism in annual and perennial plants is unknown. In the annual forb Arabidopsis thaliana and in maize (Zea mays), vegetative phase change is controlled by the sequential activity of microRNAs miR156 and miR172. miR156 is highly abundant in seedlings and decreases during the juvenile-to-adult transition, while miR172 has an opposite expression pattern. We observed similar changes in the expression of these genes in woody species with highly differentiated, well-characterized juvenile and adult phases (Acacia confusa, Acacia colei, Eucalyptus globulus, Hedera helix, Quercus acutissima), as well as in the tree Populus x canadensis, where vegetative phase change is marked by relatively minor changes in leaf morphology and internode length. Overexpression of miR156 in transgenic P. x canadensis reduced the expression of miR156-targeted SPL genes and miR172, and it drastically prolonged the juvenile phase. Our results indicate that miR156 is an evolutionarily conserved regulator of vegetative phase change in both annual herbaceous plants and perennial trees.     

Differential Expression of Hox and Notch Genes in Larval and Adult Stages of Echinococcus granulosus

This investigation aimed to evaluate the differential expression of HoxB7 and notch genes in different developmental stages of Echinococcus granulosus sensu stricto. The expression of HoxB7 gene was observed at all developmental stages. Nevertheless, significant fold differences in the expression level was documented in the juvenile worm with 3 or more proglottids, the germinal layer from infected sheep, and the adult worm from an experimentally infected dog. The notch gene was expressed at all developmental stages of E. granulosus; however, the fold difference was significantly increased at the microcysts in monophasic culture medium and the germinal layer of infected sheep in comparison with other stages. The findings demonstrated that the 2 aforementioned genes evaluated in the present study were differentially expressed at different developmental stages of the parasite and may contribute to some important biological processes of E. granulosus.     

Genome-wide identification of vegetative phase transition-associated microRNAs and target predictions using degradome sequencing in Malus hupehensis

Background

A long juvenile period between germination and flowering is a common characteristic among fruit trees, including Malus hupehensis (Pamp.) Rehd., which is an apple rootstock widely used in China. microRNAs (miRNAs) play an important role in the regulation of phase transition and reproductive growth processes.

Results

M. hupehensis RNA libraries, one adult and one juvenile phase, were constructed using tree leaves and underwent high-throughput sequencing. We identified 42 known miRNA families and 172 novel miRNAs. We also identified 127 targets for 25 known miRNA families and 168 targets for 35 unique novel miRNAs using degradome sequencing. The identified miRNA targets were categorized into 58 biological processes, and the 123 targets of known miRNAs were associated with phase transition processes. The KEGG analysis revealed that these targets were involved in starch and sucrose metabolism, and plant hormone signal transduction. Expression profiling of miRNAs and their targets indicated multiple regulatory functions in the phase transition. The higher expression level of mdm-miR156 and lower expression level of mdm-miR172 in the juvenile phase leaves implied that these two small miRNAs regulated the phase transition. mdm-miR160 and miRNA393, which regulate genes involved in auxin signal transduction, could also be involved in controlling this process. The identification of known and novel miRNAs and their targets provides new information on this regulatory process in M. hupehensis, which will contribute to the understanding of miRNA functions during growth, phase transition and reproduction in woody fruit trees.

Conclusions

The combination of sRNA and degradome sequencing can be used to better illustrate the profiling of hormone-regulated miRNAs and miRNA targets involving complex regulatory networks, which will contribute to the understanding of miRNA functions during growth, phase transition and reproductive growth in perennial woody fruit trees.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1125) contains supplementary material, which is available to authorized users.     

The MADS-box gene DAL1 is a potential mediator of the juvenile-to-adult transition in Norway spruce (Picea abies)

Progression through the plant life cycle involves change in many essential features, most notably in the capacity to reproduce. The transition from a juvenile vegetative and non-reproductive to an adult reproductive phase is gradual and can take many years; in the conifer Norway spruce, Picea abies, typically 20-25 years. We present a detailed analysis of the activities of three regulatory genes with potential roles in this transition in Norway spruce: DAL1, a MADS-box gene related to the AGL6 group of genes from angiosperms, and the two LEAFY-related genes PaLFY and PaNLY. DAL1 activity is initiated in the shoots of juvenile trees at an age of 3-5 years, and then increases with age, whereas both LFY genes are active throughout the juvenile phase. The activity of DAL1 further shows a spatial pattern along the stem of the tree that parallels a similar gradient in physiological and morphological features associated with maturation to the adult phase. Constitutive expression of DAL1 in transgenic Arabidopsis plants caused a dramatic attenuation of both juvenile and adult growth phases; flowers forming immediately after the embryonic phase of development in severely affected plants. Taken together, our results support the notion that DAL1 may have a regulatory role in the juvenile-to-adult transition in Norway spruce.     

Alternate Bearing in Citrus: Changes in the Expression of Flowering Control Genes and in Global Gene Expression in ON- versus OFF-Crop Trees

Alternate bearing (AB) is the process in fruit trees by which cycles of heavy yield (ON crop) one year are followed by a light yield (OFF crop) the next. Heavy yield usually reduces flowering intensity the following year. Despite its agricultural importance, how the developing crop influences the following year''s return bloom and yield is not fully understood. It might be assumed that an ‘AB signal’ is generated in the fruit, or in another organ that senses fruit presence, and moves into the bud to determine its fate—flowering or vegetative growth. The bud then responds to fruit presence by altering regulatory and metabolic pathways. Determining these pathways, and when they are altered, might indicate the nature of this putative AB signal. We studied bud morphology, the expression of flowering control genes, and global gene expression in ON- and OFF-crop buds. In May, shortly after flowering and fruit set, OFF-crop buds were already significantly longer than ON-crop buds. The number of differentially expressed genes was higher in May than at the other tested time points. Processes differentially expressed between ON- and OFF-crop trees included key metabolic and regulatory pathways, such as photosynthesis and secondary metabolism. The expression of genes of trehalose metabolism and flavonoid metabolism was validated by nCounter technology, and the latter was confirmed by metabolomic analysis. Among genes induced in OFF-crop trees was one homologous to SQUAMOSA PROMOTER BINDING-LIKE (SPL), which controls juvenile-to-adult and annual phase transitions, regulated by miR156. The expression pattern of SPL-like, miR156 and other flowering control genes suggested that fruit load affects bud fate, and therefore development and metabolism, a relatively long time before the flowering induction period. Results shed light on some of the metabolic and regulatory processes that are altered in ON and OFF buds.     

Morphological and physiological changes,and the functional analysis of <Emphasis Type="Italic">PdSPL9</Emphasis> in the juvenile-to-adult phase transition of <Emphasis Type="Italic">paeonia delavayi</Emphasis>

Tree peony has a long juvenile stage, which has limited breeding efforts. To date, very little information is available regarding the juvenile stage of tree peony. In the present study, Paeonia delavayi plants of varying ages were used to investigate the juvenile phase, juvenile-to-adult phase transition, and adult phase via morphological, physiological, and molecular genetic analysis. Micro-observation of buds of different ages and flower induction experiments suggested that the juvenile-to-adult phase transition of P. delavayi occurred at around 2-years of age. Plant height, crown width, leaf length, and the soluble sugar and starch content were positively correlated with plant age. The juvenile gene PdSPL9 contained miR156 targeted sites and a typical SBP domain was cloned from P. delavayi. Expression analysis showed that the expression levels of PdSPL9, PdmiR172d, and PdLFY increased with plant age, while the inverse pattern was observed for PdmiR156a. Function of PdSPL9 was further characterized in Arabidopsis plant. According to function characterization of PdSPL9 in Arabidopsis and expression patterns of PdSPL9 in P. delavayi, it was suggested that PdSPL9 plays a role in controlling juvenile-to-adult phase transition by promoting miR172d, and PdLFY expression in P. delavayi plants, while the expression of PdSPL9 is repressed by miR156a.     

Identification of differentially expressed genes in American cockroach ovaries and testes by suppression subtractive hybridization and the prediction of its miRNAs

Studies on the cockroach have contributed to our understanding of several important developmental processes, especially those that can be easily studied in the embryo. However, our knowledge on late events such as gonad differentiation in the cockroach is still limited. The major aim of the present study was to identify sex-specific genes between adult female and male Periplaneta americana. Two cDNA libraries were constructed using the suppression subtractive hybridization method; a total of 433 and 599 unique sequences were obtained from the forward library and the reverse library, respectively, by cluster assembly, and sequence alignment of 1,032 expressed sequence tags. The analysis of the differentially expressed gene functions allowed these genes to be categorized into three groups: biological process, molecular function, and cellular component. The differentially expressed genes were suggested to be related to the development of the gonads of P. americana. Twelve differentially expressed genes were randomly selected and verified using relative quantitative real-time polymerase chain reaction (qRT-PCR). Meanwhile, by adopting a range of filtering criteria, we predicted two potential microRNA sequences for P. americana, pam-miR100-3p and pam-miR7. To confirm the expression of potential microRNAs (miRNAs) in American cockroach, a qRT-PCR approach was also employed. The data presented here offer the insights into the molecular foundation of sex differences in American cockroach, and the first report for the miRNAs in this species. In addition, the results can be used as a reference for unraveling candidate genes associated with the sex and reproduction of cockroaches.     

Differential proteomic analysis during the vegetative phase change and the floral transition in Malus domestica

In order to identify the proteomic changes of apple (Malus domestica Borkh.) during the vegetative phase change and the floral transition, leaf protein of juvenile, adult vegetative and reproductive phase in a seedling ('Jonathan' × 'Golden Delicious') was extracted and analyzed by 2-D electrophoresis and Matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Seventy two gel spots with significant expression differences between ontogenetic phases were obtained. Five protein spots were only detected in leaves of juvenile phase and 11 were not; 17 spots were found exclusively in adult vegetative leaves; and only one spot solely appeared in reproductive leaves while 12 did not. Twenty six of the differentially expressed proteins identified were involved in photosynthesis. Seven enzymes were related to respiration and carbohydrate metabolism. Fifteen other proteins also presented qualitative or quantitative differences among developmental phases. The spatial distribution of one differentially expressed protein, serine hydroxymethyltransferase, was confirmed by enzyme linked immunosorbent assay and immunohistochemistry. These results strongly support the idea that the vegetative phase change and the floral transition are regulated independently during developmental process.