Temporal regulation of vegetative phase change in plants

During their vegetative growth, plants reiteratively produce leaves, buds, and internodes at the apical end of the shoot. The identity of these organs changes as the shoot develops. Some traits change gradually, but others change in a coordinated fashion, allowing shoot development to be divided into discrete juvenile and adult phases. The transition between these phases is called vegetative phase change. Historically, vegetative phase change has been studied because it is thought to be associated with an increase in reproductive competence. However, this is not true for all species; indeed, heterochronic variation in the timing of vegetative phase change and flowering has made important contributions to plant evolution. In this review, we describe the molecular mechanism of vegetative phase change, how the timing of this process is controlled by endogenous and environmental factors, and its ecological and evolutionary significance

Candidate regulators of Early Leaf Development in Maize Perturb Hormone Signalling and Secondary Cell Wall Formation When Constitutively Expressed in Rice

All grass leaves are strap-shaped with a series of parallel veins running from base to tip, but the distance between each pair of veins, and the cell-types that develop between them, differs depending on whether the plant performs C or C photosynthesis. As part of a multinational effort to introduce C traits into rice to boost crop yield, candidate regulators of C leaf anatomy were previously identified through an analysis of maize leaf transcriptomes. Here we tested the potential of 60 of those candidate genes to alter leaf anatomy in rice. In each case, transgenic rice lines were generated in which the maize gene was constitutively expressed. Lines grouped into three phenotypic classes: (1) indistinguishable from wild-type; (2) aberrant shoot and/or root growth indicating possible perturbations to hormone homeostasis; and (3) altered secondary cell wall formation. One of the genes in class 3 defines a novel monocot-specific family. None of the genes were individually sufficient to induce C -like vein patterning or cell-type differentiation in rice. A better understanding of gene function in C plants is now needed to inform more sophisticated engineering attempts to alter leaf anatomy in C plants

Proper activity of the age-dependent miR156 is required for leaf heteroblasty and extrafloral nectary development in Passiflora spp

Passion flower extrafloral nectaries (EFNs) protrude from leaves and facilitate mutualistic interactions with insects; however, how age cues control EFN growth remains poorly under- stood.Here, we examined leaf and EFN morphology and development of two Passiflora species with distinct leaf shapes, and compared the phenotype of these to transgenics with manipulated activity of the age-dependent miR156, which targets several SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL) transcription factors.Low levels of miR156 correlated with leaf maturation and EFN formation in Passiflora edulis and P. cincinnata. Accordingly, manipulating miR156 activity affected leaf heteroblasty and EFN development. miR156-overexpressing leaves exhibited less abundant and tiny EFNs in both Passiflora species. EFN abundance remained mostly unchanged when miR156 activity was reduced, but it led to larger EFNs in P. cincinnata. Transcriptome analysis of young leaf primordia revealed that miR156-targeted SPLs may be required to properly express leaf and EFN-associated genes. Importantly, altered miR156 activity impacted sugar profiles of the nectar and modified ecological relationships between EFNs and ants.Our work provides evidence that the miR156/SPL module indirectly regulates EFN development in an age-dependent manner and that the EFN development program is closely associated with the heteroblastic developmental program of the EFN-bearing leaves

Candidate regulators of Early Leaf Development in Maize Perturb Hormone Signalling and Secondary Cell Wall Formation When Constitutively Expressed in Rice

All grass leaves are strap-shaped with a series of parallel veins running from base to tip, but the distance between each pair of veins, and the cell-types that develop between them, differs depending on whether the plant performs C or C photosynthesis. As part of a multinational effort to introduce C traits into rice to boost crop yield, candidate regulators of C leaf anatomy were previously identified through an analysis of maize leaf transcriptomes. Here we tested the potential of 60 of those candidate genes to alter leaf anatomy in rice. In each case, transgenic rice lines were generated in which the maize gene was constitutively expressed. Lines grouped into three phenotypic classes: (1) indistinguishable from wild-type; (2) aberrant shoot and/or root growth indicating possible perturbations to hormone homeostasis; and (3) altered secondary cell wall formation. One of the genes in class 3 defines a novel monocot-specific family. None of the genes were individually sufficient to induce C -like vein patterning or cell-type differentiation in rice. A better understanding of gene function in C plants is now needed to inform more sophisticated engineering attempts to alter leaf anatomy in C plants

Partnering to improve public transport in developing countries

This paper demonstrates the importance of—and potential for—partnerships between the private and public sectors, and citizen groups, as a crucial means towards the improvement of public transport services in the developing world. It draws mainly upon the research findings of case studies in Karachi, Faisalabad, Dar es Salaam and Colombo between 1999 and 2003. The paper looks at some of the factors that need to be taken into consideration if a partnership is to be successful, before demonstrating the potential of existing links between users, operators and regulators. The potential for partnerships to improve upon the existing situation emerged on several occasions during the research, and these are summarised. Later sections look at the types of partnership that might be encouraged in the transport sector, as well as the importance of nurturing and supporting such partnerships. Finally, the paper highlights priorities for intervention—in the areas of infrastructure investment, land use and employment strategy, regulation and stakeholder collaboration—and the role partnerships could play in these interventions. The paper concludes with the importance of strengthening existing partnerships in public transport provision and creating and developing new ones. In this respect the authors consider it crucial that policymakers give due consideration to partnering approaches in the future

Fundamental Science Investigations to Develop a 6-MV Laser Triggered Gas Switch for ZR: First Annual Report.

In October 2005, an intensive three-year Laser Triggered Gas Switch (LTGS) development program was initiated to investigate and solve observed performance and reliability issues with the LTGS for ZR. The approach taken has been one of mission-focused research: to revisit and reassess the design, to establish a fundamental understanding of LTGS operation and failure modes, and to test evolving operational hypotheses. This effort is aimed toward deploying an initial switch for ZR in 2007, on supporting rolling upgrades to ZR as the technology can be developed, and to prepare with scientific understanding for the even higher voltage switches anticipated needed for future high-yield accelerators. The ZR LTGS was identified as a potential area of concern quite early, but since initial assessments performed on a simplified Switch Test Bed (STB) at 5 MV showed 300-shot lifetimes on multiple switch builds, this component was judged acceptable. When the Z{sub 20} engineering module was brought online in October 2003 frequent flashovers of the plastic switch envelope were observed at the increased stresses required to compensate for the programmatically increased ZR load inductance. As of October 2006, there have been 1423 Z{sub 20} shots assessing a variety of LTGS designs. Numerous incremental and fundamental switch design modifications have been investigated. As we continue to investigate the LTGS, the basic science of plastic surface tracking, laser triggering, cascade breakdown, and optics degradation remain high-priority mission-focused research topics. Significant progress has been made and, while the switch does not yet achieve design requirements, we are on the path to develop successively better switches for rolling upgrade improvements to ZR. This report summarizes the work performed in FY 2006 by the large team. A high-level summary is followed by detailed individual topical reports