MADS-box genes active in developing pollen cones of Norway spruce (Picea abies) are homologous to the B-class floral homeotic genes in angiosperms.

The reproductive organs of conifers, the pollen cones and seed cones, differ in morphology from the angiosperm flower in several fundamental respects. In this report we present evidence to suggest that the two plant groups, in spite of these morphological differences and the long evolutionary distance between them, share important features in regulating the development of the reproductive organs. We present the cloning of three genes, DAL11, DAL12, and DAL13, from Norway spruce, all of which are related to the angiosperm B-class of homeotic genes. The B-class genes determine the identities of petals and stamens. They are members of a family of MADS-box genes, which also includes C-class genes that act to determine the identity of carpels and, in concert with B genes specify stamens in the angiosperm flower. Phylogenetic analyses and the presence of B-class specific C-terminal motifs in the DAL protein sequences imply homology to the B-class genes. Specific expression of all three genes in developing pollen cones suggests that the genes are involved in one aspect of B function, the regulation of development of the pollen-bearing organs. The different temporal and spatial expression patterns of the three DAL genes in the developing pollen cones indicate that the genes have attained at least in part distinct functions. The DAL11, DAL12, and 13 expression patterns in the pollen cone partly overlap with that of the previously identified DAL2 gene, which is structurally and functionally related to the angiosperm C-class genes. This result supports the hypothesis that an interaction between B- and C-type genes is required for male organ development in conifers like in the angiosperms. Taken together, our data suggests that central components in the regulatory mechanisms for reproductive organ development are conserved between conifers and angiosperms and, thus, among all seed plants.     

Conifer reproductive development involves B-type MADS-box genes with distinct and different activities in male organ primordia

The Norway spruce MADS-box genes DAL11, DAL12 and DAL13 are phylogenetically related to the angiosperm B-function MADS-box genes: genes that act together with A-function genes in specifying petal identity and with C-function genes in specifying stamen identity to floral organs. In this report we present evidence to suggest that the B-gene function in the specification of identity of the pollen-bearing organs has been conserved between conifers and angiosperms. Expression of DAL11 or DAL12 in transgenic Arabidopsis causes phenotypic changes which partly resemble those caused by ectopic expression of the endogenous B-genes. In similar experiments, flowers of Arabidopsis plants expressing DAL13 showed a different homeotic change in that they formed ectopic anthers in whorls one, two or four. We also demonstrate the capacity of the spruce gene products to form homodimers, and that DAL11 and DAL13 may form heterodimers with each other and with the Arabidopsis B-protein AP3, but not with PI, the second B-gene product in Arabidopsis. In situ hybridization experiments show that the conifer B-like genes are expressed specifically in developing pollen cones, but differ in both temporal and spatial distribution patterns. These results suggest that the B-function in conifers is dual and is separated into a meristem identity and an organ identity function, the latter function possibly being independent of an interaction with the C-function. Thus, even though an ancestral B-function may have acted in combination with C to specify micro- and megasporangia, the B-function has evolved differently in conifers and angiosperms.     

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.     

<Emphasis Type="Italic">APETALA2</Emphasis> like genes from <Emphasis Type="Italic">Picea abies</Emphasis> show functional similarities to their Arabidopsis homologues

In angiosperm flower development the identity of the floral organs is determined by the A, B and C factors. Here we present the characterisation of three homologues of the A class gene APETALA2 (AP2) from the conifer Picea abies (Norway spruce), Picea abies APETALA2 LIKE1 (PaAP2L1), PaAP2L2 and PaAP2L3. Similar to AP2 these genes contain sequence motifs complementary to miRNA172 that has been shown to regulate AP2 in Arabidopsis. The genes display distinct expression patterns during plant development; in the female-cone bud PaAP2L1 and PaAP2L3 are expressed in the seed-bearing ovuliferous scale in a pattern complementary to each other, and overlapping with the expression of the C class-related gene DAL2. To study the function of PaAP2L1 and PaAP2L2 the genes were expressed in Arabidopsis. The transgenic PaAP2L2 plants were stunted and flowered later than control plants. Flowers were indeterminate and produced an excess of floral organs most severely in the two inner whorls, associated with an ectopic expression of the meristem-regulating gene WUSCHEL. No homeotic changes in floral-organ identities occurred, but in the ap2-1 mutant background PaAP2L2 was able to promote petal identity, indicating that the spruce AP2 gene has the capacity to substitute for an A class gene in Arabidopsis. In spite of the long evolutionary distance between angiosperms and gymnosperms and the fact that gymnosperms lack structures homologous to sepals and petals our data supports a functional conservation of AP2 genes among the seed plants.     

Distribution of eriophyoid mites (Acari: Eriophyoidea) on coniferous trees

The aim of the paper was to determine the infestation parameters and species composition of eriophyoid mites for different parts of Norway spruce and Scots pine as well as for different age groups of the trees. The observations on the occurrence of the mites were conducted in 2004 and 2005 in 4 locations distributed in various regions of Poland, accounting for 11 environments (location x year). Three plant age groups were studied: (1) adult trees: 40–60 years old, additionally divided into three levels: top, middle and bottom; (2) young trees: 6–10 years old; and (3) seedlings: 2–3 years old. The same number of species (five) occurred on each coniferous tree, but only one, the rarest, was common on both tree species. Out of 500 samples for each species, mites were found on 279 pine (55.8%) and 252 spruce samples (50.2%). No tendency for the mites to choose any particular level on Scots pine and Norway spruce was observed. In addition, no tendency for the mites to choose trees from any of the age groups was observed for both Scots pine and Norway spruce, in the latter case the result obtained also for mite species subdivided into vagrant and refuge-seeking ones. Final conclusions were that in case of adult trees samples can be taken from the bottom part of a tree; however, sampling from young trees growing among adult trees may be seen as the most efficient sampling method.     

拟南芥叶片数目变化突变体对营养生长时相转变的影响

拟南芥(Arabidopsis thaliana)的营养生长可以分为2个阶段: 幼龄期与成熟期。由幼龄期向成熟期的转变(VPC)与叶片的形态学特征、茎顶端分生组织(SAM)形状、远轴面表皮毛的出现以及SPL家族转录因子表达水平的变化相关。研究表明, 造成这种转变的信号来源于叶原基。该研究利用2种莲座叶数目改变了的突变体和对野生型切除叶片的方法, 分析了叶片数目对VPC的影响。结果表明, 莲座叶数目的减少推迟了VPC的发生; 而莲座叶数目增多突变体amp1-1并未使VPC的发生提前, 推测叶源信号的产生受到了光合作用的影响。     

A Norway spruce FLOWERING LOCUS T homolog is implicated in control of growth rhythm in conifers

Growth in perennial plants possesses an annual cycle of active growth and dormancy that is controlled by environmental factors, mainly photoperiod and temperature. In conifers and other nonangiosperm species, the molecular mechanisms behind these responses are currently unknown. In Norway spruce (Picea abies L. Karst.) seedlings, growth cessation and bud set are induced by short days and plants from southern latitudes require at least 7 to 10 h of darkness, whereas plants from northern latitudes need only 2 to 3 h of darkness. Bud burst, on the other hand, is almost exclusively controlled by temperature. To test the possible role of Norway spruce FLOWERING LOCUS T (FT)-like genes in growth rhythm, we have studied expression patterns of four Norway spruce FT family genes in two populations with a divergent bud set response under various photoperiodic conditions. Our data show a significant and tight correlation between growth rhythm (both bud set and bud burst), and expression pattern of one of the four Norway spruce phosphatidylethanolamine-binding protein gene family members (PaFT4) over a variety of experimental conditions. This study strongly suggests that one Norway spruce homolog to the FT gene, which controls flowering in angiosperms, is also a key integrator of photoperiodic and thermal signals in the control of growth rhythms in gymnosperms. The data also indicate that the divergent adaptive bud set responses of northern and southern Norway spruce populations, both to photoperiod and light quality, are mediated through PaFT4. These results provide a major advance in our understanding of the molecular control of a major adaptive trait in conifers and a tool for further molecular studies of adaptive variation in plants.     

Regulatory circuit for responses of nitrogen catabolic gene expression to the GLN3 and DAL80 proteins and nitrogen catabolite repression in Saccharomyces cerevisiae.

We demonstrate that expression of the UGA1, CAN1, GAP1, PUT1, PUT2, PUT4, and DAL4 genes is sensitive to nitrogen catabolite repression. The expression of all these genes, with the exception of UGA1 and PUT2, also required a functional GLN3 protein. In addition, GLN3 protein was required for expression of the DAL1, DAL2, DAL7, GDH1, and GDH2 genes. The UGA1, CAN1, GAP1, and DAL4 genes markedly increased their expression when the DAL80 locus, encoding a negative regulatory element, was disrupted. Expression of the GDH1, PUT1, PUT2, and PUT4 genes also responded to DAL80 disruption, but much more modestly. Expression of GLN1 and GDH2 exhibited parallel responses to the provision of asparagine and glutamine as nitrogen sources but did not follow the regulatory responses noted above for the nitrogen catabolic genes such as DAL5. Steady-state mRNA levels of both genes did not significantly decrease when glutamine was provided as nitrogen source but were lowered by the provision of asparagine. They also did not respond to disruption of DAL80.     

Propagation of Norway spruce via somatic embryogenesis

Somatic embryogenesis combined with cryopreservation is an attractive method to propagate Norway spruce (Picea abies) vegetatively both as a tool in the breeding programme and for large-scale clonal propagation of elite material. Somatic embryos are also a valuable tool for studying regulation of embryo development. Embryogenic cell lines of Norway spruce are established from zygotic embryos. The cell lines proliferate as proembryogenic masses (PEMs). Somatic embryos develop from PEMs. PEM-to-somatic embryo transition is a key developmental switch that determines the yield and quality of mature somatic embryos. Withdrawal of plant growth regulators (PGRs) stimulates PEM-to-somatic embryo transition accompanied by programmed cell death (PCD) in PEMs. This PCD is mediated by a marked decrease in extracellular pH. If the acidification is abolished by buffering the culture medium, PEM-to-somatic embryo transition together with PCD is inhibited. Cell death, induced by withdrawal of PGRs, can be suppressed by extra supply of lipo-chitooligosaccharides (LCOs). Extracellular chitinases are probably involved in production and degradation of LCOs. During early embryogeny, the embryos form an embryonal mass surrounded by a surface layer. The formation of a surface layer is accompanied by a switch in the expression pattern of an Ltp-like gene (Pa18) and a homeobox gene (PaHB1), from ubiquitous expression in PEMs to surface layer-specific in somatic embryos. Ectopic expression of Pa18 and PaHB1 leads to an early developmental block. Transgenic embryos and plants of Norway spruce are routinely produced by using a biolistic approach. The transgenic material is used for studying the importance of specific genes for regulating plant development, but transgenic plants can also be used for identification of candidate genes for use in the breeding programme.     

The Arabidopsis compact inflorescence genes: phase-specific growth regulation and the determination of inflorescence architecture

During their life cycle, higher plants pass through a series of growth phases that are characterized by the production of morphologically distinct vegetative and reproductive organs and by different growth patterns. Three major phases have been described in Arabidopsis: juvenile vegetative, adult vegetative, and reproductive. In this report we describe a novel, phase-specific mutant in Arabidopsis, compact inflorescence (cif). The most apparent aspect of the cif phenotype is a strong reduction in the elongation of internodes in the inflorescence, resulting in the formation of a floral cluster at the apical end of all reproductive shoots. Elongation and expansion of adult vegetative rosette leaves are also compromised in mutant plants. The onset of the cif trait correlates closely with morphological changes marking the phase transition from juvenile to adult, and mutant plants produce normal flowers and are fully fertile. Hence the cif phenotype appears to be adult vegetative phase-specific. Histological sections of mutant inflorescence internodes indicate normal tissue specification, but reduced cell elongation compared to wild-type. compact inflorescence is inherited as a two-gene trait involving the action of a recessive and a dominant locus. These two cif genes appear to be key components of a growth regulatory pathway that is closely linked to phase change, and specifies critical aspects of plant growth and architecture including inflorescence internode length.     

Gibberellins promote vegetative phase change and reproductive maturity in maize.

Postembryonic shoot development in maize (Zea mays L.) is divided into a juvenile vegetative phase, an adult vegetative phase, and a reproductive phase that differ in the expression of many morphological traits. A reduction in the endogenous levels of bioactive gibberellins (GAs) conditioned by any one of the dwarf1, dwarf3, dwarf5, or another ear1 mutations in maize delays the transition from juvenile vegetative to adult vegetative development and from adult vegetative to reproductive development. Mutant plants cease producing juvenile traits (e.g. epicuticular wax) and begin producing adult traits (e.g. epidermal hairs) later than wild-type plants. They also cease producing leaves and begin producing reproductive structures later than wild-type plants. These mutations greatly enhance most aspects of the phenotype of Teopod1 and Teopod2, suggesting that GAs suppress part but not all of the Teopod phenotype. Application of GA3 to Teopod2 mutants and Teopod1, dwarf3 double mutants confirms this result. We conclude that GAs act in conjunction with several other factors to promote both vegetative and reproductive maturation but affect different developmental phases unequally. Furthermore, the GAs that regulate vegetative and reproductive maturation, like those responsible for stem elongation, are downstream of GA20 in the GA biosynthetic pathway.     

Microarray analysis of vegetative phase change in maize

Vegetative phase change is the developmental transition from the juvenile phase to the adult phase in which a plant becomes competent for sexual reproduction. The gain of ability to flower is often accompanied by changes in patterns of differentiation in newly forming vegetative organs. In maize, juvenile leaves differ from adult leaves in morphology, anatomy and cell wall composition. Whereas the normal sequence of juvenile followed by adult is repeated with every sexual generation, this sequence can be altered in maize by the isolation and culture of the shoot apex from an adult phase plant: an 'adult' meristem so treated reverts to forming juvenile vegetative organs. To begin to unravel the as-yet poorly understood molecular mechanisms underlying phase change in maize, we compared gene expression in two juvenile sample types, leaf 4 and culture-derived leaves 3 or 4, with an adult sample type (leaf 9) using cDNA microarrays. All samples were leaf primordia at plastochron 6. A gene was scored as 'phase induced' if it was up- or downregulated in both juvenile sample types, compared with the adult sample type, with at least a twofold change in gene expression at a P-value of < or =0.005. Some 221 expressed sequence tags (ESTs) were upregulated in juveniles, and 28 ESTs were upregulated in adults. The largest class of juvenile-induced genes was comprised of those involved in photosynthesis, suggesting that maize plants are primed for energy production early in vegetative growth by the developmental induction of photosynthetic genes.     

Identification of a gene involved in the juvenile-to-adult transition (JAT) in cultivated olive trees

The juvenile-to-adult transition is a complex and poorly understood process in plant development required to reach reproductive competence. For woody plants, knowledge of this transition is even scantier and no genes have been definitively identified as involved in this transition. To search for genes involved in the juvenile-to-adult transition in olive, we constructed juvenile and adult subtractive cDNA gene libraries and identified genes that were differentially expressed in the juvenile and adult phases. In the analysis of theses libraries, we found 13 differentially expressed genes. One of these genes designated as juvenile to adult transition (JAT) was of special interest because it was highly expressed at the mRNA level in the early developmental phases but repressed in the adult phase. The analysis of mutant trees altered in the juvenile-to-adult transition, as well as a segregating progeny of 31 trees from a “Picual” x “Jabaluna” cross, support the contention that its activity might be required for a non-delayed transition. The study of an Arabidopsis thaliana JAT mutant strain confirmed this hypothesis as it showed a delayed flowering phenotype. JAT is expressed in different parts of the plant, showing an unexpectedly high level of mRNA in the roots. However, the JAT expression level is not determined by the distance to the roots, but rather depends on the developmental stage of the branch meristems. JAT is a widely represented gene in plants that appears to be involved in the control of the juvenile-to-adult transition in olive.     

MicroRNA gene regulation cascades during early stages of plant development

MicroRNAs (miRNAs) regulate various developmental programs of plants. This review focuses on miRNA involvement in early events of plant development, such as seed germination, seedling development and the juvenile to adult phase transition. miR159 and miR160 are involved in the regulation of seed germination through their effects on the sensitivity of seeds to ABA. miR156 and miR172 play critical roles in the emergence of vegetative leaves at post-germinative stages, which is important for the transition to autotrophic growth. The phase transition from the juvenile to adult stage in both monocots and dicots is also regulated by miR156 and miR172. In these early developmental processes, there are miRNA gene regulation cascades where the miR156 pathway acts upstream of the miR172 pathway. Moreover, targets of miR156 and miR172 exert positive feedback on the expression of MIR genes that suppress themselves. The early events of plant development appear to be controlled by complex mechanisms involving sequential expression of different miRNA pathways and feedback loops among miRNAs and their target genes.     

Population divergence for heteroblasty in the Canary Island pine (Pinus canariensis, Pinaceae)

A heteroblastic (or vegetative phase) change is an abrupt manifestation in the general heteroblastic development during the ontogeny of plants. The Canary Island pine undergoes an especially marked and delayed heteroblastic change, including both the formation of secondary needles on dwarf shoots and the onset of preformed growth. To assess genetic and environmental effects on the heteroblastic change in this species, we followed plants from 19 populations at a dry site and a wetter site. Comparing juvenile and adult needles from the same individuals, the adult had a significantly lower rate of water loss and higher leaf mass per area. Pooling data from all seed sources, the heteroblastic change took place when plants reached a critical height, on average, at 4 years of age at the dry site and 1 year earlier at the wet site. Within a subsample of individuals of equal size, mortality was significantly higher in juvenile plants than in mature plants. However, the juvenile phase was longer in plants from dry regions when compared to plants from highly productive, wet regions. This apparent contradiction might be explained through differential resource allocation and the cost of sclerophylly and resprouting ability. Considering the life strategy of the Canary Island pine, we interpret the prolonged juvenile phase as an unavoidable trade-off for the high tolerance of adults to harsh environments.