Prolonged Juvenile Phase Research Articles

Genetic Structure in the Northern Range Margins of Common Ash, Fraxinus excelsior L.

During post glacial colonization, loss of genetic diversity due to leading edge effects may be attenuated in forest trees because of their prolonged juvenile phase, allowing many migrants to reach the colonizing front before populations become reproductive. The northern range margins of temperate tree taxa in Europe are particularly suitable to study the genetic processes that follow colonization because they have been little affected by northern refugia. Here we examined how post glacial range dynamics have shaped the genetic structure of common ash (Fraxinus excelsior L.) in its northern range compared to its central range in Europe. We used four chloroplast and six nuclear microsatellites to screen 42 populations (1099 trees), half of which corresponded to newly sampled populations in the northern range and half of which represented reference populations from the central range obtained from previously studies. We found that northern range populations of common ash have the same chloroplast haplotypes as south-eastern European populations, suggesting that colonization of the northern range took place along a single migration route, a result confirmed by the structure at the nuclear microsatellites. Along this route, diversity strongly decreased only in the northern range, concomitantly with increasing population differentiation and complex population substructures, a pattern consistent with a leading edge colonization model. Our study highlights that while diversity is maintained in the central range of common ash due to broad colonizing fronts and high levels of gene flow, it profoundly decreases in the northern range, where colonization was unidirectional and probably involved repeated founder events and population fluctuations. Currently, common ash is threatened by ash dieback, and our results on northern populations will be valuable for developing gene conservation strategies.

Over-Expression of FT1 in Plum (Prunus domestica) Results in Phenotypes Compatible with Spaceflight: A Potential New Candidate Crop for Bioregenerative Life Support Systems

ABSTRACT Tree fruits (e.g., apples, plums, cherries) are appealing constituents of a crew menu for long-duration exploration missions (i.e., Mars), both in terms of their nutritive and menu diversity contributions. Although appealing, tree fruit species have long been precluded as candidate crops for use in plant-based bioregenerative life support system designs based on their large crown architecture, prolonged juvenile phase, and phenological constraints. Recent advances by researchers at the United States Department of Agriculture (USDA) have led to the development of plum (Prunus domestica) trees ectopically over-expressing the Flowering Locus T-1 (FT1) gene from Populus trichocarpa (poplar). The transformed plants exhibit atypical phenotypes that seemingly eliminate the aforementioned obstacles to spaceflight. Here we demonstrate the FT1 expression system (FasTrack) and the resultant dwarf growth habits, early flowering, and continuous fruit production. The potential contribution of P. domestica as a countermeasure to microgravity-induced bone loss is also discussed.

TheCOP1OrthologPPSRegulates the Juvenile–Adult and Vegetative–Reproductive Phase Changes in Rice

Because plant reproductive development occurs only in adult plants, the juvenile-to-adult phase change is an indispensable part of the plant life cycle. We identified two allelic mutants, peter pan syndrome-1 (pps-1) and pps-2, that prolong the juvenile phase in rice (Oryza sativa) and showed that rice PPS is an ortholog of Arabidopsis thaliana CONSTITUTIVE PHOTOMORPHOGENIC1. The pps-1 mutant exhibits delayed expression of miR156 and miR172 and the suppression of GA biosynthetic genes, reducing the GA(3) content in this mutant. In spite of its prolonged juvenile phase, the pps-1 mutant flowers early, and this is associated with derepression of RAP1B expression in pps-1 plants independently of the Hd1-Hd3a/RFT1 photoperiodic pathway. PPS is strongly expressed in the fourth and fifth leaves, suggesting that it regulates the onset of the adult phase downstream of MORI1 and upstream of miR156 and miR172. Its ability to regulate the vegetative phase change and the time of flowering suggests that rice PPS acquired novel functions during the evolution of rice/monocots.

Colonization processes and the maintenance of genetic diversity: insights from a pioneer rainforest tree,Aucoumea klaineana

Despite recurrent episodes of range expansion and contraction, forest trees often harbour high genetic diversity. Studies of temperate forest trees suggest that prolonged juvenile phase and high pollen flow are the main factors limiting founder effects. Here, we studied the local colonization process of a pioneer rainforest tree in central Africa, Aucoumea klaineana. We identified 87% of parents among trees up to 20-25 years old and could thus compare direct parentage structure data with classical population genetics estimators. In this species, genetic diversity was maintained during colonization. The absence of founder effects was explained by (i) local random mating and (ii) local recruitment, as we showed that 75% of the trees in the close neighbourhood participated in the recruitment of new saplings. Long-distance pollen flow contributed little to genetic diversity: pollen and seed dispersal was mainly within stand (128 and 118 m, respectively). Spatial genetic structure was explained by aggregated seed dispersal rather than by mother-offspring proximity as assumed in classical isolation-by-distance models. Hence, A. klaineana presents a genetic diversity pattern typical of forest trees but does not follow the classical rules by which this diversity is generally achieved. We suggest that while high local genetic variability is of general importance to forest tree survival, the proximate mechanisms by which it is achieved may follow very different scenarios.

The first genetic maps of cashew (Anacardium occidentale L.)

Cashew (Anacardium occidentale) is a widespread tropical tree crop that is grown primarily for its nuts and has a global production of over 2 million Mt. In spite of its economic importance to many countries, however, no linkage map containing STS anchor sites has yet been produced for this species. This is largely attributable to a prolonged juvenile phase of the tree (limiting mapping to F1 progenies) and difficulty in effecting sufficient hand-pollinations to create mapping populations of effective size. Here, we produce an F1 mapping population of 85 individuals from a cross between CP 1001 (dwarf commercial clone) and CP 96 (giant genotype), and use it to generate two linkage genetic maps comprising of 205 genetic markers (194 AFLP and 11 SSR markers). The female map (CP 1001) contains 122 markers over 19 linkage groups and the male map (CP 96) comprises 120 markers assembled over 23 linkage groups. The total map distance of the female map is 1050.7 cM representing around 68% genome coverage, whereas the male map spans 944.7 cM (64% coverage). The average map distance between markers is 8.6 cM in the female map and 7.9 cM in the male map. Homology between the two maps was established between 13 linkage groups of the female map and 14 of the male map using 46 bridging markers that include 11 SSR markers. These maps represent a platform from which to identify loci controlling economically important traits in this crop.

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.

Foraging Ontogeny is not Linked to Delayed Maturation in Squirrel Monkeys (Saimiri sciureus)

AbstractThe acquisition of complex foraging behaviors by young is a proposed cause of a prolonged juvenile phase in many vertebrates, including primates. I compared the foraging behaviors of infant, juvenile and adult squirrel monkeys to determine if significant age‐related differences in foraging behavior and efficiency were present. Infants and juveniles differed from each other in patterns of prey and fruit foraging, but few differences existed between juveniles and adults. Despite differing in the use of foraging substrates, young juveniles (8–12 mo) were as efficient as older juveniles (1–4 yr) and adults at capturing and processing large prey. Young juveniles (<1 yr) were limited in their ability to consume husked palm fruits due to an inability to peel them to obtain pulp. By 1 yr of age, however, foraging behaviors of adults and juveniles were nearly indistinguishable. The absence of meaningful differences between adults and juvenile foraging is not consistent with the hypothesis that the need to develop foraging skills accounts for the pattern of extended juvenility in squirrel monkeys.

Alterations in endogenous levels of cytokinins following grafting of Pinus radiatasupport ratio of cytokinins as an index of ageing and vigour

Markers for ageing or maturation in woody plants provides the possibility of identifying genotypes with a prolonged juvenile phase, or to evaluate reinvigoration procedures, such as grafting of adult material. This study focuses specifically on cytokinins (Cks) as markers, due to their role in the transition process from juvenile to adult states. Previous reports from our group disclosed that the ratio of isopentenyladenine-type (iP-type) to zeatin-type (Z-type) Cks decreases during tree maturation, a maturation and ageing index being likely in Pinus radiata. Based on these results, Cks were tested in terminal buds of adult and grafted adult P. radiata material to corroborate the importance of the aforementioned balance as an index in the reinvigoration process of adult trees associated with grafting procedures. Results revealed the reversion of this index pattern parallel to the reactivation of some juvenile traits, namely, increasing values of the ratio throughout the reinvigoration process. According to previous results, however, the opposite was the case during the reverse process. This fact allowed us to validate the iP-type/Z-type Ck ratio as an ageing and vigour index.

The role of gonadal steroids in feedback regulation of gonadotropin secretion at different stages of primate development.

The serum gonadotropin response to castration was assessed in 8 foetal, 2 neonatal, 30 juvenile, and 2 adult rhesus monkeys (M. mulatta). In the 30 castrated juvenile monkeys and 8 sham-operated controls, concentrations of oestrone, oestradiol, androstenedione, dihydrotestosterone, testosterone and 17OH-progesterone were measured in 10 ml serum pools before, one month after, and one year after the surgical procedure. Castration during foetal life (83-137 days gestation) was followed within 48-72 h by a significant rise in serum FSH levels in males, but had no effect on the already high levels in females. Similarly, castration of males during the first post-natal month raised serum FSH and LH into the adult castrate range; however, after 3 months of age serum gonadotropin levels again declined to the normal juvenile range in spite of the open feedback loop. Orchiectomy of prepubertal juvenile monkeys (age 3 month-2 8/12 years) had no immediate effect on serum gonadotropins, but was followed by a delayed rise in FSH (at age 2 3/12-4 3/12 years) and LH (at age 2 7/12-4 4/12 years) to adult castrate levels. Orchiectomy of older prepubertal (by serum testosterone) or adult males resulted within a few days in a progressive and sustained rise in serum FSH and a more gradual rise in LH. Prepubertal gonadotropin regulation appeared to be sexually dimorphic, since ovariectomy in juvenile females (age 3 months-1 5/12 years) was followed by generally elevated, if somewhat erratic, serum FSH values, with a secondary rise in both FSH and LH levels at 2-2 1/12 years. In both sexes, prepubertal castration caused a significant and sustained decline in serum concentrations of oestradiol; castrated males also showed a decline in serum testosterone levels. Although prepubertal castration also caused in both sexes a slight decline in serum oestrone, and ovariectomy a decline in serum androstenedione and dihydrotestosterone, these effects were not sustained one year later, and values were not significantly different from sham-operated controls. Taken together, these data lend support to a model of primate sexual maturation in which the primary regulator of gonadotropin secretion in both sexes during the prolonged juvenile phase is central inhibition of the hypothalamic GnRH regulator. However, during foetal and neonatal life, and again following the onset of puberty, the major modulator of gonadotropin secretion becomes sex steroid-mediated feedback inhibition.

A Technique of Shoot Apex Grafting and Its Utilization Towards Recovering Virus-free Citrus Clones1

Abstract Shoot apices, excised from Citrus cultivars of known virus content, were successfully grafted in vitro onto disease-free rootstock seedlings and some virus-free plants were obtained. The prolonged juvenile phase which characterizes disease-free nucellar lines was bypassed by this procedure.