The tomato hexokinase LeHXK1 cloning, mapping, expression pattern and phylogenetic relationships

Dai, Nir; Kandel-Kfir, Michal; Petreikov, Marina; Hanael, Rana; Levin, Ilan; Ricard, Bérénice; Rothan, Christophe; Schaffer, Arthur A.; Granot, David

doi:10.1016/s0168-9452(02)00166-8

Cited by 37 publications

(41 citation statements)

References 30 publications

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“…Free fructose must Wrst be phosphorylated by either hexokinase (HXK) or fructokinase (FRK) for further metabolism, otherwise, the accumulating fructose might feedback inhibit SuSy activity, reducing sucrose cleavage . HXK and FRK are distinguished by their substrate speciWcities and aYnities (Renz and Stitt 1993;Dai et al 2002b;Granot 2007). HXK may phosphorylate both glucose and fructose, but its aYnity to fructose is two orders of magnitude lower than its aYnity to glucose, as well as two orders of magnitude lower than the aYnity of FRK to fructose.…”

Section: Introductionmentioning

confidence: 99%

LeFRK2 is required for phloem and xylem differentiation and the transport of both sugar and water

Damari-Weissler

Rachamilevitch

Aloni

et al. 2009

Planta

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It has been suggested that LeFRK2, the major fructose-phosphorylating enzyme in tomato plants, may be required for stem xylem development. Yet, we do not know if this enzyme affects the development of individual vessels, whether it affects water conductance, or whether it affects phloem development and sugar transport. Here, we show that suppression of LeFRK2 results in a significant reduction in the size of vascular cells and slows fiber maturation. The vessels in stems of LeFRK2-antisense plants are narrower than in WT plants and have thinner secondary cell walls. Although the cambium produces rounded secondary vessels, these vessels become deformed during the early stages of xylem maturation. Water conductance is then reduced in stems, roots, and leaves, suggesting that LeFRK2 influences xylem development throughout the entire vascular system. Interestingly, the build-up of positive xylem pressure under static (no-flow) conditions was also decreased. Suppression of LeFRK2 reduced the length and width of the sieve elements, as well as callose deposition. To examine the effect of LeFRK2 suppression on phloem transport, we created triple-grafted plants in which a portion of the wild-type stem was replaced with an antisense interstcok, and compared the contents of the transported sugar, sucrose, in the different portions of these stems. Sucrose contents above and within the LeFRK2-antisense interstock were significantly higher than those below the graft. These results show that the antisense interstock restricted the downward movement of sucrose, suggesting that LeFRK2 is required for both phloem and xylem development.

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Section: Introductionmentioning

confidence: 99%

LeFRK2 is required for phloem and xylem differentiation and the transport of both sugar and water

Damari-Weissler

Rachamilevitch

Aloni

et al. 2009

Planta

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“…3 and 4, it can be surmised that, despite the mild decrease in starch in some of the antisense lines, FK exhibits very little control over this pathway. Although physiologically very distinct, it is interesting to compare these data with those reported for transgenic tomato in which the antisense inhibition of the tomato homolog of StFK1 was carried out (Dai et al 2002a). The repression of FK in the tomato also did not have an adverse effect on starch yield, and increases of starch were even reported in young fruits of the FK-deficient lines.…”

Section: Effect Of Manipulation Of Fructokinase Activity On Tuber Metmentioning

confidence: 96%

“…The exception to this statement is the analysis of FKs from tomato, performed in some detail by Bennett and co-workers (Kanayama et al 1998, Dai et al 2002a, Odanaka et al 2002, German et al 2003. In an initial study, they established that the two major tomato isoforms differed in both their regulation by substrate and their spatial location, suggesting that the highly regulated form (FKII) was most probably involved in starch metabolism (Kanayama et al 1998).…”

Section: Introductionmentioning

confidence: 99%

Modulation of Fructokinase Activity of Potato (Solanum tuberosum) Results in Substantial Shifts in Tuber Metabolism

Davies¹,

Shepherd²,

Burrell

et al. 2005

Plant and Cell Physiology

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;Potato plants (Solanum tuberosum L. cvs Desiree and Record) transformed with sense and antisense constructs of a cDNA encoding the potato fructokinase StFK1 exhibited altered transcription of this gene, altered amount of protein and altered enzyme activities. Measurement of the maximal catalytic activity of fructokinase revealed a 2-fold variation in leaf (from 90 to 180% of wild type activity) and either a 10-or 30-fold variation in tuber (from 10 or 30% to 300% in Record and Desiree, respectively) activity. The comparative effect of the antisense construct in leaf and tuber tissue suggests that this isoform is only a minor contributor to the total fructokinase activity in the leaf but the predominant isoform in the tuber. Antisense inhibition of the fructokinase resulted in a reduced tuber yield; however, its overexpression had no impact on this parameter. The modulation of fructokinase activity had few, consistent effects on carbohydrate levels, with the exception of a general increase in glucose content in the antisense lines, suggesting that this enzyme is not important for the control of starch synthesis. However, when metabolic fluxes were estimated, it became apparent that the transgenic lines display a marked shift in metabolism, with the rate of redistribution of radiolabel to sucrose markedly affected by the activity of fructokinase. These data suggest an important role for fructokinase, acting in concert with sucrose synthase, in maintaining a balance between sucrose synthesis and degradation by a mechanism independent of that controlled by the hexose phosphate-mediated activation of sucrose phosphate synthase.

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“…Kandel-KWr and H. Damari-Weissler contributed equally to this work. hexokinase isozymes were reported in a wide range of plant species and tissues including pea seeds and leaves (Turner et al 1977;Dry et al 1983), wheatgerm (Higgins and Easterby 1974), developing seeds of Ricinus communis (Miernyk and Dennis 1983), maize kernels and roots (Doehlert 1989;da-Silva et al 2001), developing potato tubers (Renz et al 1993), rice embryos (Guglielminetti et al 2000), celery root tips and petioles (Yamamoto et al 2000), pollen grains of bell pepper (Karni and Aloni 2002) and tomato fruits (Menu et al 2001;Dai et al 2002). Yet, most of the biochemical studies were carried out without pre-knowledge about the number and sequence of the genes encoding hexokinases in each species and the tissues in which they are expressed.…”

Section: Introductionmentioning

confidence: 99%

Two newly identified membrane-associated and plastidic tomato HXKs: characteristics, predicted structure and intracellular localization

Kandel-Kfir

Damari-Weissler

German

et al. 2006

Planta

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Two new tomato hexokinase genes, LeHXK3 and LeHXK4, were cloned and characterized, placing tomato as the first plant with four characterized HXK genes. Based on their sequence, LeHXK3 is the third membrane-associated (type-B) and LeHXK4 is the first plastidic (type-A) HXK identified in tomato. Expression of HXK-GFP fusion proteins in protoplasts indicated that the LeHxk3 enzyme is associated with the mitochondria while LeHxk4 is localized in plastids. Furthermore, LeHxk4::GFP fusion protein is found within stromules, suggesting transport of LeHxk4 between plastids. Structure prediction of the various plant HXK enzymes suggests that unlike the plastidic HXKs, the predicted membrane-associated HXKs are positively charged near their putative N-terminal membrane anchor domain, which might enhance their association with the negatively charged membranes. LeHxk3 and LeHxk4 were analyzed following expression in yeast. Both enzymes have higher affinity for glucose relative to fructose and are inhibited by ADP. Yet, unlike the other HXKs, the stromal HXK has higher Vmax with glucose than with fructose. Expression analysis of the four HXK genes in tomato tissues demonstrated that LeHXK1 and LeHXK4 are the dominant HXKs in all tissues examined. Notably, the plastidic LeHXK4 is expressed in all tissues including starchless, non-photosynthetic sink tissues, such as pink and red fruits, implying phosphorylation of imported hexoses in plastids. It has been suggested that trehalose 6-phosphate (T6P) might inhibit HXK activity. However, none of the yeast-expressed tomato HXK genes was sensitive either to T6P or to trehalose, suggesting that unlike fungi HXKs, plant HXKs are not regulated by T6P.

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The tomato hexokinase LeHXK1 cloning, mapping, expression pattern and phylogenetic relationships

Cited by 37 publications

References 30 publications

LeFRK2 is required for phloem and xylem differentiation and the transport of both sugar and water

LeFRK2 is required for phloem and xylem differentiation and the transport of both sugar and water

Modulation of Fructokinase Activity of Potato (Solanum tuberosum) Results in Substantial Shifts in Tuber Metabolism

Two newly identified membrane-associated and plastidic tomato HXKs: characteristics, predicted structure and intracellular localization

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