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Dual florigen response in potatoes The seasonality of plant developmental processes such as flowering and tuber formation is dependent largely on changes in day length. This response is mediated in Arabidopsis , tomato and rice plants by a mobile protein known as FLOWERING LOCUS T (FT), the main component of the long-range florigen signal. A study of the potato ( Solanum tuberosum ) now shows that floral and tuberization transitions are controlled by two different FT -like genes ( StSP3D and StSP6A ) that respond to independent environmental cues. Seasonal fluctuations in day length regulate important aspects of plant development such as the flowering transition or, in potato ( Solanum tuberosum ), the formation of tubers. Day length is sensed by the leaves, which produce a mobile signal transported to the shoot apex or underground stems to induce a flowering transition or, respectively, a tuberization transition. Work in Arabidopsis, tomato and rice ( Oryza sativa ) identified the mobile FLOWERING LOCUS T (FT) protein as a main component of the long-range ‘florigen’, or flowering hormone, signal 1 , 2 , 3 . Here we show that expression of the Hd3a gene, the FT orthologue in rice, induces strict short-day potato types 4 to tuberize in long days. Tuber induction is graft transmissible and the Hd3a–GFP protein is detected in the stolons of grafted plants, transport of the fusion protein thus correlating with tuber formation. We provide evidence showing that the potato floral and tuberization transitions are controlled by two different FT -like paralogues (St SP3D and St SP6A ) that respond to independent environmental cues, and show that an autorelay mechanism involving CONSTANS modulates expression of the tuberization-control St SP6A gene.

Grafting is an ancient cloning method that has been used widely for thousands of years in agricultural practices. Graft-union development is also an intricate process that involves substantial changes such as organ regeneration and genetic material exchange. However, the molecular mechanisms for graft-union development are still largely unknown. Here, a micrografting method that has been used widely in Arabidopsis was improved to adapt it a smooth procedure to facilitate sample analysis and to allow it to easily be applied to various dicotyledonous plants. The developmental stage of the graft union was characterized based on this method. Histological analysis suggested that the transport activities of vasculature were recovered at 3 days after grafting (dag) and that auxin modulated the vascular reconnection at 2 dag. Microarray data revealed a signal-exchange process between cells of the scion and stock at 1 dag, which re-established the communication network in the graft union. This process was concomitant with the clearing of cell debris, and both processes were initiated by a wound-induced programme. The results demonstrate the feasibility and potential power of investigating various plant developmental processes by this method, and represent a primary and significant step in interpretation of the molecular mechanisms underlying graft-union development.

Sustainable intensification is seen as the main route for meeting the world’s increasing demands for food and fibre. As demands mount for greater efficiency in the use of resources to achieve this goal, so the focus on roots and rootstocks and their role in acquiring water and nutrients, and overcoming pests and pathogens, is increasing. The purpose of this review is to explore some of the ways in which understanding root systems and their interactions with soils could contribute to the development of more sustainable systems of intensive production. Physical interactions with soil particles limit root growth if soils are dense, but root–soil contact is essential for optimal growth and uptake of water and nutrients. X-ray microtomography demonstrated that maize roots elongated more rapidly with increasing root–soil contact, as long as mechanical impedance was not limiting root elongation, while lupin was less sensitive to changes in root–soil contact. In addition to selecting for root architecture and rhizosphere properties, the growth of many plants in cultivated systems is profoundly affected by selection of an appropriate rootstock. Several mechanisms for scion control by rootstocks have been suggested, but the causal signals are still uncertain and may differ between crop species. Linkage map locations for quantitative trait loci for disease resistance and other traits of interest in rootstock breeding are becoming available. Designing root systems and rootstocks for specific environments is becoming a feasible target.

Vitis vinifera scions are commonly grafted onto rootstocks of other grape species to influence scion vigour and provide resistance to soil-borne pests and abiotic stress; however, the mechanisms by which rootstocks affect scion physiology remain unknown. This study characterized the hydraulic physiology of Vitis rootstocks that vary in vigour classification by investigating aquaporin (VvPIP) gene expression, fine-root hydraulic conductivity (Lp r ), % aquaporin contribution to Lp r , scion transpiration, and the size of root systems. Expression of several VvPIP genes was consistently greater in higher-vigour rootstocks under favourable growing conditions in a variety of media and in root tips compared to mature fine roots. Similar to VvPIP expression patterns, fine-root Lp r and % aquaporin contribution to Lp r determined under both osmotic (Lp r Osm ) and hydrostatic (Lp r Hyd ) pressure gradients were consistently greater in high-vigour rootstocks. Interestingly, the % aquaporin contribution was nearly identical for Lp r Osm and Lp r Hyd even though a hydrostatic gradient would induce a predominant flow across the apoplastic pathway. In common scion greenhouse experiments, leaf area-specific transpiration (E) and total leaf area increased with rootstock vigour and were positively correlated with fine-root Lp r . These results suggest that increased canopy water demands for scion grafted onto high-vigour rootstocks are matched by adjustments in root-system hydraulic conductivity through the combination of fine-root Lp r and increased root surface area.

Knowledge about the root system structure and the uptake efficiency of root orders is critical to understand the adaptive plasticity of plants towards salt stress. Thus, this study describes the phenological and physiological plasticity of Citrus volkameriana rootstocks under severe NaCl stress on the level of root orders. Phenotypic root traits known to influence uptake processes, for example frequency of root orders, specific root area, cortical thickness, and xylem traits, did not change homogeneously throughout the root system, but changes after 6 months under 90 mM NaCl stress were root order specific. Chloride accumulation significantly increased with decreasing root order, and the Cl(-) concentration in lower root orders exceeded those in leaves. Water flux densities of first-order roots decreased to <20% under salinity and did not recover after stress release. The water flux densities of higher root orders changed marginally under salinity and increased 2- to 6-fold in second and third root orders after short-term stress release. Changes in root order frequency, morphology, and anatomy indicate rapid and major modification of C. volkameriana root systems under salt stress. Reduced water uptake under salinity was related to changes of water flux densities among root orders and to reduced root surface areas. The importance of root orders for water uptake changed under salinity from root tips towards higher root orders. The root order-specific changes reflect differences in vulnerability (indicated by the salt accumulation) and ontogenetic status, and point to functional differences among root orders under high salinity.

Grapevine rupestris stem pitting-associated virus (GRSPaV) is a widespread virus infecting Vitis spp. Although it has established a compatible viral interaction in Vitis vinifera without the development of phenotypic alterations, it can occur as distinct variants that show different symptoms in diverse Vitis species. The changes induced by GRSPaV in V. vinifera cv 'Bosco', an Italian white grape variety, were investigated by combining agronomic, physiological, and molecular approaches, in order to provide comprehensive information about the global effects of GRSPaV. In two years, this virus caused a moderate decrease in physiological efficiency, yield performance, and sugar content in berries associated with several transcriptomic alterations. Transcript profiles were analysed by a microarray technique in petiole, leaf, and berry samples collected at véraison and by real-time RT-PCR in a time course carried out at five grapevine developmental stages. Global gene expression analyses showed that transcriptomic changes were highly variable among the different organs and the different phenological phases. GRSPaV triggers some unique responses in the grapevine at véraison, never reported before for other plant-virus interactions. These responses include an increase in transcripts involved in photosynthesis and CO(2) fixation, a moderate reduction in the photosynthesis rate and some defence mechanisms, and an overlap with responses to water and salinity stresses. It is hypothesized that the long co-existence of grapevine and GRSPaV has resulted in the evolution of a form of mutual adaptation between the virus and its host. This study contributes to elucidating alternative mechanisms used by infected plants to contend with viruses.

Several dwarf plum genotypes (Prunus salicina L.), due to deficiency of unknown gibberellin (GA) signalling, were identified. A cDNA encoding GA 2-oxidase (PslGA2ox), the major gibberellin catabolic enzyme in plants, was cloned and used to screen the GA-deficient hybrids. This resulted in the identification of a dwarf plum hybrid, designated as DGO24, that exhibits a markedly elevated PslGA2ox signal. Grafting 'Early Golden' (EG), a commercial plum cultivar, on DGO24 (EG/D) enhanced PslGA2ox accumulation in the scion part and generated trees of compact stature. Assessment of active GAs in such trees revealed that DGO24 and EG/D accumulated relatively much lower quantities of main bioactive GAs (GA(1) and GA(4)) than control trees (EG/M). Moreover, the physiological function of PslGA2ox was studied by determining the molecular and developmental consequences due to ectopic expression in Arabidopsis. Among several lines, two groups of homozygous transgenics that exhibited contrasting phenotypes were identified. Group-1 displayed a dwarf growth pattern typical of mutants with a GA deficiency including smaller leaves, shorter stems, and delay in the development of reproductive events. In contrast, Group-2 exhibited a 'GA overdose' phenotype as all the plants showed elongated growth, a typical response to GA application, even under limited GA conditions, potentially due to co-suppression of closely related Arabidopsis homologous. The studies reveal the possibility of utilizing PslGA2ox as a marker for developing size-controlling rootstocks in Prunus.

Background Rose is recognized as an important ornamental plant worldwide, and it is also one of the most widely used flowers in gardens. At present, the improvement of rose traits is still difficult and uncertain, and molecular breeding can provide new ideas for the improvement of modern rose varieties. Somatic embryos are quite good receptors for genetic transformation. However, little is known about the molecular mechanisms underlying during the regeneration process of rose somatic embryos. To elucidate the molecular regulation mechanism of somatic embryo plantlet regeneration, the relationship between the differences in traits of the two different regenerated materials and the significantly differentially expressed genes (DEGs) related to phytohormone pathways in the process of regeneration were be investigated. Results These representative two regenerated samples from single-piece cotyledonary somatic embryo (SPC) culture of Rosa hybrida ‘John F. Kennedy’, were harvested for transcriptome analysis, with the SPC explants at the initial culture (Day 0) as the control. The differentially expressed genes (DEGs) in the materials from two different types for regeneration approach (SBF type: the regeneration approach type of single bud formed from SPC explants; MBF type: the regeneration approach type of multiple buds formed from SPC explants) were be screened by means of the transcriptome sequencing technology. In this study, a total of about 396.24 million clean reads were obtained, of which 78.95–82.92% were localized to the reference genome, compared with the initial material (CK sample), there were 5594 specific genes in the material of SBF type and 6142 specific genes in the MBF type. The DEGs from the SBF type material were mainly concentrated in the biological processes of GO terms such as phytohormones, substance transport, cell differentiation, and redox reaction. The KEGG enrichment analysis revealed these DEGs were more active in ubiquinone and other terpenoid-quinone biosynthesis, fatty acid elongation, steroid biosynthesis, and glycosphingolipid biosynthesis-globo and isoglobo series. In contrast, the DEGs induced by the MBF type material were mainly associated with the biological processes such as phytohormones, phosphorylation, photosynthesis and signal transduction. According to KEGG analysis, these DEGs of MBF type were significantly enriched in the porphyrin and chlorophyll metabolism, brassinosteroid biosynthesis, carotenoid biosynthesis, and peroxisome. Furthermore, the results from the phytohormone pathways analysis showed that the auxin-responsive factor SAUR and the cell wall modifying enzyme gene XTH were upregulated for expression but the protein phosphatase gene PP2C was downregulated for expression in SBF type; the higher expression of the ethylene receptor ETR, the ethylene transduction genes EBF1/2 , the transcription factor EIN3, and the ethylene-responsive transcription factor ERF1/2 were induced by MBF type. Conclusions According to the GO and KEGG analysis, it indicated the DEGs between two different regenerated materials from somatic embryos were significantly different which might be causing morphological differences. That was somatic embryos from Rosa hybrida ‘John F. Kennedy’ could regenerate plantlet via both classic somatic embryogenesis (seed-like germination) and organogenesis, cotyledonary somatic embryos should be considered as one kind of intermediate materials similiar to callus, rather than the indicator materials for somatic embryogenesis.

To evaluate the role of root-synthesized ABA in regulating growth and stomatal behaviour under well-watered conditions, isogenic wild-type (WT) and ABA-deficient flacca (flc) tomato (Solanum lycopersicum) were reciprocally and self-grafted just below the cotyledonary node. Since flc scions had lower leaf water potentials due to higher transpiration rates, a subset of all graft combinations was grown under a shoot misting treatment to minimize differences in shoot water status. Misting did not alter the relative effects of the different graft combinations on leaf area. WT scions had the greatest leaf area and lowest whole plant transpiration rate irrespective of the rootstock, implying that shoot ABA biosynthesis was sufficient to account for a WT shoot phenotype. In WT scions, the rootstock had no effect on detached leaf ethylene evolution or xylem concentrations of ABA or the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). In flc scions, although the WT rootstock suppressed stomatal conductance of individual leaves, there was no detectable effect on whole plant transpiration rate. However, leaf area of flc/WT (scion/rootstock) plants increased 1.6-fold compared to flc self-grafts. WT rootstocks increased xylem ABA concentration in flc scions (relative to flc self-grafts) up to 3-fold, and resulted in xylem ACC concentrations and detached leaf ethylene evolution similar to WT scions. Since the WT rootstock normalized shoot ethylene relations but only partially restored the leaf area of flc scions (relative to that of WT scions), shoot ABA biosynthesis can directly promote leaf area via an unknown, ethylene-independent, mechanism.

The intensity of the root-sourced abscisic acid (ABA) signal has long been thought to decrease along its longdistance transport pathway, and hence the shoot responses to the ABA signal would be expected to become less sensitive with the increase in plant height. It is reported here that there is a significant modification of the ABA signal intensity in its pathway to leaves in grapevine (Vitis riparia x× itis labrusca), but in contrast to the expectation that the ABA signal intensity may decrease along its long-distance transport pathway, it was found that the root-sourced ABA signal is gradually intensified along a vine for as long as 3 m under both water-stressed and non-stressed conditions. Consistent with the alterations in ABA signal intensity, stomatal sensitivity to a root-sourced ABA signal was also gradually increased from the base to the apex. Leaf stomatal conductance near the apex was more severely inhibited than in the leaves at the base of the vine. It was observed that xylem pH was significantly increased from the base to the apex, and that artificially changing the xylem sap pH to be more alkaline by feeding with buffers increased the xylem ABA concentration. Our results suggest that the pH gradient along the stem may play a role in the modification and enhancement of ABA signal intensity such that the stomata at the top of canopy can be more sensitively regulated in response to soil drying.