Special Issue: Plant vascular biology (2)   

June 2017, Volume 59 Issue 6, Pages 349每449.

Cover Caption: Plant vascular biology (2)
The cover shows secondary vascular bundles, produced by a unique monocot cambium, in which the phloem is centrally-located, surrounded by a xylem ring (Zinkgraf et al., 436每449). In this issue, first insights into the genetic regulation and evolution of this fascinating meristem are presented in support of the hypothesis that genes regulating this vascular cambia were coopted in the evolution of this novel meristem that is found within some species of the Asparagales.


Announcement: Changes in the JIPB board  
Author: Chun-Ming Liu
Journal of Integrative Plant Biology 2017 59(6): 350每353
Published Online: May 18, 2017
DOI: 10.1111/jipb.12553
Abstract (Browse 443)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
The plant vascular system II: From resource allocation, inter-organ communication and defense, to evolution of the monocot cambium  
Author: William J. Lucas and Chun-Ming Liu
Journal of Integrative Plant Biology 2017 59(6): 354每355
Published Online: May 3, 2017
DOI: 10.1111/jipb.12551
Abstract (Browse 403)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
          Invited Expert Review
Plant xylem hydraulics: What we understand, current research, and future challenges  
Author: Martin D. Venturas, John S. Sperry and Uwe G. Hacke
Journal of Integrative Plant Biology 2017 59(6): 356每389
Published Online: March 14, 2017
DOI: 10.1111/jipb.12534

Herein we review the current state-of-the-art of plant hydraulics in the context of plant physiology, ecology, and evolution, focusing on current and future research opportunities. We explain the physics of water transport in plants and the limits of this transport system, highlighting the relationships between xylem structure and function. We describe the great variety of techniques existing for evaluating xylem resistance to cavitation. We address several methodological issues and their connection with current debates on conduit refilling and exponentially shaped vulnerability curves. We analyze the trade-offs existing between water transport safety and efficiency. We also stress how little information is available on molecular biology of cavitation and the potential role of aquaporins in conduit refilling. Finally, we draw attention to how plant hydraulic traits can be used for modeling stomatal responses to environmental variables and climate change, including drought mortality.

Abstract (Browse 435)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Water is transported in xylem conduits from the soil to the leaves under negative pressures. This is a metabolically inexpensive transport system but it is subjected to the risk of cavitation failure. Herein we address methodologies for measuring xylem resistance to cavitation, current debates, and future research opportunities in plant hydraulics.
          Research Articles
Sucrose transporter2 contributes to maize growth, development, and crop yield  
Author: Kristen A Leach, Thu M Tran, Thomas L Slewinski, Robert B Meeley and David M Braun
Journal of Integrative Plant Biology 2017 59(6): 390每408
Published Online: February 16, 2017
DOI: 10.1111/jipb.12527

During daylight, plants produce excess photosynthates, including sucrose, which is temporarily stored in the vacuole. At night, plants remobilize sucrose to sustain metabolism and growth. Based on homology to other sucrose transporter (SUT) proteins, we hypothesized the maize (Zea mays) SUCROSE TRANSPORTER2 (ZmSUT2) protein functions as a sucrose/H+ symporter on the vacuolar membrane to export transiently stored sucrose. To understand the biological role of ZmSut2, we examined its spatial and temporal gene expression, determined the protein subcellular localization, and characterized loss-of-function mutations. ZmSut2 mRNA was ubiquitously expressed and exhibited diurnal cycling in transcript abundance. Expressing a translational fusion of ZmSUT2 fused to a red fluorescent protein in maize mesophyll cell protoplasts revealed that the protein localized to the tonoplast. Under field conditions, zmsut2 mutant plants grew slower, possessed smaller tassels and ears, and produced fewer kernels when compared to wild-type siblings. zmsut2 mutants also accumulated two-fold more sucrose, glucose, and fructose as well as starch in source leaves compared to wild type. These findings suggest (i) ZmSUT2 functions to remobilize sucrose out of the vacuole for subsequent use in growing tissues; and (ii) its function provides an important contribution to maize development and agronomic yield.

Abstract (Browse 547)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
In this study, the role of ZmSUT2, a maize vacuolar sucrose transport system, in carbon partitioning and crop yield is demonstrated. During the day, plants transiently store excess sucrose in vacuoles. Assays show that ZmSUT2 functions in sucrose export from the vacuole into the cytoplasm. Mutant maize plants lacking ZmSut2 have reduced growth, accumulate sugars and starch in their leaves, and have reduced crop yield.
Implications of nitrogen phloem loading for carbon metabolism and transport during Arabidopsis development  
Author: James P. Santiago and Mechthild Tegeder
Journal of Integrative Plant Biology 2017 59(6): 409每421
Published Online: March 14, 2017
DOI: 10.1111/jipb.12533

Metabolite transport processes and primary metabolism are highly interconnected. This study examined the importance of source-to-sink nitrogen partitioning, and associated nitrogen metabolism for carbon capture, transport and usage. Specifically, Arabidopsis aap8 (AMINO ACID PERMEASE 8) mutant lines were analyzed to resolve the consequences of reduced amino acid phloem loading for source leaf carbon metabolism, sucrose phloem transport and sink development during vegetative and reproductive growth phase. Results showed that decreased amino acid transport had a negative effect on sink development of aap8 lines throughout the life cycle, leading to an overall decrease in plant biomass. During vegetative stage, photosynthesis and carbohydrate levels were decreased in aap8 leaves, while expression of carbon metabolism and transport genes, as well as sucrose phloem transport were not affected despite reduced sink strength. However, when aap8 plants transitioned to reproductive phase, carbon fixation and assimilation as well as sucrose partitioning to siliques were strongly decreased. Overall, this work demonstrates that phloem loading of nitrogen has varying implications for carbon fixation, assimilation and source-to-sink allocation depending on plant growth stage. It further suggests alterations in source-sink relationships, and regulation of carbon metabolism and transport by sink strength in a development-dependent manner.

Abstract (Browse 535)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
This study examines the relationship between nitrogen phloem loading, leaf carbon metabolism and sucrose partitioning during vegetative and reproductive growth phases of Arabidopsis. This work established that nitrogen transport processes have important implications for carbon fixation, assimilation and source-to-sink allocation, depending on plant growth stage.
The fungal UmSrt1 and maize ZmSUT1 sucrose transporters battle for plant sugar resources  
Author: Anke Wittek, Ingo Dreyer, Khaled A.S. Al-Rasheid, Norbert Sauer, Rainer Hedrich and Dietmar Geiger
Journal of Integrative Plant Biology 2017 59(6): 422每435
Published Online: March 15, 2017
DOI: 10.1111/jipb.12535

The biotrophic fungus Ustilago maydis causes corn smut disease, inducing tumor formation in its host Zea mays. Upon infection, the fungal hyphae invaginate the plasma membrane of infected maize cells, establishing an interface where pathogen and host are separated only by their plasma membranes. At this interface the fungal and maize sucrose transporters, UmSrt1 and ZmSUT1, compete for extracellular sucrose in the corn smut/maize pathosystem. Here we biophysically characterized ZmSUT1 and UmSrt1 in Xenopus oocytes with respect to their voltage-, pH- and substrate-dependence and determined affinities toward protons and sucrose. In contrast to ZmSUT1, UmSrt1 has a high affinity for sucrose and is relatively pH- and voltage-independent. Using these quantitative parameters, we developed a mathematical model to simulate the competition for extracellular sucrose at the contact zone between the fungus and the host plant. This approach revealed that UmSrt1 exploits the apoplastic sucrose resource, which forces the plant transporter into a sucrose export mode providing the fungus with sugar from the phloem. Importantly, the high sucrose concentration in the phloem appeared disadvantageous for the ZmSUT1, preventing sucrose recovery from the apoplastic space in the fungus/plant interface.

Abstract (Browse 540)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
The corn smut fungus exploits the sugar resources of its maize host and negatively affects yield and food quality. At the plant/pathogen interface, maize and corn smut sucrose transporters battle for plant sugar resources. Here, a combination of biophysical studies and mathematical simulations was employed to analyze this 'arms race' between plant and fungus.
Transcript profiling of a novel plant meristem, the monocot cambium  
Author: Matthew Zinkgraf, Suzanne Gerttula and Andrew Groover
Journal of Integrative Plant Biology 2017 59(6): 436每449
Published Online: March 17, 2017
DOI: 10.1111/jipb.12538

While monocots lack the ability to produce a vascular cambium or woody growth, some monocot lineages evolved a novel lateral meristem, the monocot cambium, which supports secondary radial growth of stems. In contrast to the vascular cambium found in woody angiosperm and gymnosperm species, the monocot cambium produces secondary vascular bundles, which have an amphivasal organization of tracheids encircling a central strand of phloem. Currently there is no information concerning the molecular genetic basis of the development or evolution of the monocot cambium. Here we report high-quality transcriptomes for monocot cambium and early derivative tissues in two monocot genera, Yucca and Cordyline. Monocot cambium transcript profiles were compared to those of vascular cambia and secondary xylem tissues of two forest tree species, Populus trichocarpa and Eucalyptus grandis. Monocot cambium transcript levels showed that there are extensive overlaps between the regulation of monocot cambia and vascular cambia. Candidate regulatory genes that vary between the monocot and vascular cambia were also identified, and included members of the KANADI and CLE families involved in polarity and cell-cell signaling, respectively. We suggest that the monocot cambium may have evolved in part through reactivation of genetic mechanisms involved in vascular cambium regulation.

Abstract (Browse 549)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
This study explores the evolution of a novel monocot cambium through transcriptomics analysis of secondary (cambial) meristematic tissues collected from the monocots, Yucca and Cordyline, and the forest trees, poplar and Eucalyptus. Evidence is presented for the cooption of gene regulatory networks that enables some monocots to form a lateral meristem, thereby allowing them to grow in girth and make tree-like forms.



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