The Pitfalls of Transgenic Selection and New Roles of<i>AtHXK1</i>: A High Level of<i>AtHXK1</i>Expression Uncouples Hexokinase1-Dependent Sugar Signaling from Exogenous Sugar

Kelly, Gilor; David‐Schwartz, Rakefet; Sade, Nir; Moshelion, Menachem; Levi, A.; Alchanatis, V.; Granot, David

doi:10.1104/pp.112.196105

Cited by 75 publications

(65 citation statements)

References 32 publications

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“…This release of buds by exogenous sucrose in intact or decapitated plants is consistent with the increased bud growth observed in isolated rose stem segments supplied with sugars (30,31) and in plants with genetically altered sugar signaling and/or metabolism (32). Our results indicate that enhancing sugar supply to axillary buds is sufficient for bud release (Fig.…”

Section: Sucrose Supply Promotes Bud Release and Inhibits Branched1supporting

confidence: 74%

Sugar demand, not auxin, is the initial regulator of apical dominance

Mason

Ross

Babst

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

481

510

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For almost a century the plant hormone auxin has been central to theories on apical dominance, whereby the growing shoot tip suppresses the growth of the axillary buds below. According to the classic model, the auxin indole-3-acetic acid is produced in the shoot tip and transported down the stem, where it inhibits bud growth. We report here that the initiation of bud growth after shoot tip loss cannot be dependent on apical auxin supply because we observe bud release up to 24 h before changes in auxin content in the adjacent stem. After the loss of the shoot tip, sugars are rapidly redistributed over large distances and accumulate in axillary buds within a timeframe that correlates with bud release. Moreover, artificially increasing sucrose levels in plants represses the expression of BRANCHED1 (BRC1), the key transcriptional regulator responsible for maintaining bud dormancy, and results in rapid bud release. An enhancement in sugar supply is both necessary and sufficient for suppressed buds to be released from apical dominance. Our data support a theory of apical dominance whereby the shoot tip's strong demand for sugars inhibits axillary bud outgrowth by limiting the amount of sugar translocated to those buds.shoot branching | sink demand | decapitation | girdling | long-distance signaling

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Section: Sucrose Supply Promotes Bud Release and Inhibits Branched1supporting

confidence: 74%

Sugar demand, not auxin, is the initial regulator of apical dominance

Mason

Ross

Babst

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

481

510

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“…Importantly, it was shown that catalytically inactive HXK1 mutant forms still have a signaling function, supporting the view that the role of HKX1 in signaling high sugar availability is independent of its role in Glc metabolism (Moore et al, 2003). More recent work has shown that HXK1 also mediates stomatal closure, thereby contributing to the feedback effect of sugar accumulation on photosynthesis (Kelly et al, 2012;Kelly et al, 2013).…”

mentioning

confidence: 55%

“…Within the cells, HXK1-dependent signaling is involved in senescence regulation. Transgenic tomato (Dai et al, 1999;Swartzberg et al, 2011) and Arabidopsis (Kelly et al, 2012) plants overexpressing the Arabidopsis HXK1 have accelerated senescence, whereas the HXK1 mutant gin2-1 shows delayed senescence (Moore et al, 2003) and a reduced senescence response to Glc treatment . While these findings support a role of HXK1 signaling in senescence regulation, a lack of HXK1 does not completely abolish the effect of sugar treatment on senescence, suggesting that other signaling pathways are involved.…”

Section: Senescencementioning

confidence: 99%

“…In addition to T6P, HXK1 is involved in increased branching, as suggested by a loss of apical dominance in transgenic HXK1-overexpressing Arabidopsis plants (Kelly et al, 2012). Mutations in genes encoding proteins that interact with TOR also suggest a function of TOR-dependent signaling in the regulation of apical dominance and shoot branching: Mutants in Raptor (Anderson et al, 2005) or LST8 (Moreau et al, 2012) have increased shoot branching, suggesting that the TOR pathway may inhibit shoot branching, although how this may affect the response to sugar availability has not been investigated.…”

Section: Shoot Branchingmentioning

confidence: 99%

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Transitioning to the Next Phase: The Role of Sugar Signaling throughout the Plant Life Cycle

Wingler

2017

Plant Physiol.

141

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“…Overexpression of maize (Zea mays) NAD-malic enzyme in tobacco resulted in plants with a decrease in g s but gains in biomass, suggesting that manipulation of both stomata and mesophyll processes could improve plant WUE (La Porte et al, 2002). Finally, Kelly et al (2012) increased the expression of hexokinase in guard cells with the counterintuitive effect of decreasing g s . Hexokinase drives starch breakdown through the phosphorylation of Glc, which then feeds into glycolysis, the tricarboxylic acid cycle, and malic acid synthesis.…”

Section: Engineering Stomatal Signaling and Metabolismmentioning

confidence: 99%

Stomatal Size, Speed, and Responsiveness Impact on Photosynthesis and Water Use Efficiency

2014

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The control of gaseous exchange between the leaf and bulk atmosphere by stomata governs CO 2 uptake for photosynthesis and transpiration, determining plant productivity and water use efficiency. The balance between these two processes depends on stomatal responses to environmental and internal cues and the synchrony of stomatal behavior relative to mesophyll demands for CO 2 . Here we examine the rapidity of stomatal responses with attention to their relationship to photosynthetic CO 2 uptake and the consequences for water use. We discuss the influence of anatomical characteristics on the velocity of changes in stomatal conductance and explore the potential for manipulating the physical as well as physiological characteristics of stomatal guard cells in order to accelerate stomatal movements in synchrony with mesophyll CO 2 demand and to improve water use efficiency without substantial cost to photosynthetic carbon fixation. We conclude that manipulating guard cell transport and metabolism is just as, if not more likely to yield useful benefits as manipulations of their physical and anatomical characteristics. Achieving these benefits should be greatly facilitated by quantitative systems analysis that connects directly the molecular properties of the guard cells to their function in the field.In order for plants to function efficiently, they must balance gaseous exchange between inside and outside the leaf to maximize CO 2 uptake for photosynthetic carbon assimilation (A) and to minimize water loss through transpiration. Stomata are the "gatekeepers" responsible for all gaseous diffusion, and they adjust to both internal and external environmental stimuli governing CO 2 uptake and water loss. The pathway for CO 2 uptake from the bulk atmosphere to the site of fixation is determined by a series of diffusional resistances, which start with the layer of air immediately surrounding the leaf (the boundary layer). Stomatal pores provide a major resistance to flux from the atmosphere to the substomatal cavity within the leaf. Further resistance is encountered by CO 2 across the aqueous and lipid boundaries into the mesophyll cell and chloroplasts (mesophyll resistance). Water leaving the leaf largely follows the same pathway in reverse, but without the mesophyll resistance component. Guard cells surround the stomatal pore. They increase or decrease in volume in response to external and internal stimuli, and the resulting changes in guard cell shape adjust stomatal aperture and thereby affect the flux of gases between the leaf internal environment and the bulk atmosphere. Stomatal behavior, therefore, controls the volume of CO 2 entering the intercellular air spaces of the leaf for photosynthesis. It also plays a key role in minimizing the amount of water lost. Transpiration, by virtue of the concentration differences, is an order of magnitude greater than CO 2 uptake, which is an inevitable consequence of free diffusion across this pathway. Although the cumulative area of stomatal pores only represents a small fraction...

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The Pitfalls of Transgenic Selection and New Roles ofAtHXK1: A High Level ofAtHXK1Expression Uncouples Hexokinase1-Dependent Sugar Signaling from Exogenous Sugar

Cited by 75 publications

References 32 publications

Sugar demand, not auxin, is the initial regulator of apical dominance

Sugar demand, not auxin, is the initial regulator of apical dominance

Transitioning to the Next Phase: The Role of Sugar Signaling throughout the Plant Life Cycle

Stomatal Size, Speed, and Responsiveness Impact on Photosynthesis and Water Use Efficiency

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