LeFRK4, a novel tomato (Lycopersicon esculentum Mill.) fructokinase specifically expressed in stamens

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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.

Section: Introductionmentioning

confidence: 99%

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

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“…The predominantly expressed isoform in tomato fruits of all three accessions was fk2, as was described before by German et al (2002) for S. lycopersicum. Notably, S. habrochaites lacked fk1 expression (the minor form of fructokinase in the fruits) but had a higher fk2 expression level during early development.…”

Section: Regulation Of Gene Expressionmentioning

confidence: 69%

Differences in regulation of carbohydrate metabolism during early fruit development between domesticated tomato and two wild relatives

Kortstee

Appeldoorn

Oortwijn

et al. 2007

Early development and growth of fruit in the domesticated tomato Solanum lycopersicum cultivar Money Maker and two of its wild relatives, S. peruvianum LA0385 and S. habrochaites LA1777, were studied. Although small diVerences exist, the processes involved and the sequence of events in fruit development are similar in all three species. The growth of developing fruits is exponential and the relative growth rate accelerates from 5 days after pollination (DAP 5) to DAP 8, followed by a decline during further development. Growth is positively correlated to the standard "Brix plus starch'' in the period DAP 8-DAP 20. Carbohydrate composition and levels of sugars and organic acids diVer in fruits of the wild accessions compared to domesticated tomato. The wild accessions accumulate sucrose instead of glucose and fructose, and ripe fruits contain higher levels of malate and citrate. The enzymes responsible for the accumulation of glucose and fructose in domesticated tomatoes are soluble invertase and sucrose synthase. The regulation of initial carbohydrate metabolism in the domesticated tomato diVers from that in the wild species, as could be concluded from measuring activities of enzymes involved in primary carbohydrate metabolism. Furthermore, changes in the activity of several enzymes, e.g., cell wall invertase, soluble invertase, fructokinase and phosphoglucomutase, could be attributed to changes in gene expression level. For other enzymes, additional control mechanisms play a role in the developing tomato fruits. Localization by in-situ activity staining of enzymes showed comparable results for fruits of domesticated tomato and the wild accessions. However, in the pericarp of S. peruvianum, less activity staining of phosphogluco-isomerase, phosphoglucomutase and UDPglucosepyrophosphorylase was observed.

“…Although several FRK isozymes and an increasing number of novel FRK genes have been characterized (Taylor et al 1995;Kanayama et al 1997;Gonzali et al 2001;German et al 2002German et al , 2004Jiang et al 2003;Zhang et al 2003), the number of FRK genes in various species and their speciWc roles are still unknown. In tomato, four FRK genes, LeFRK1-4, have been identiWed.…”

Section: Introductionmentioning

confidence: 99%

“…Three of them, LeFRK1-3, correspond to the three isozymes found in tomato fruits Dai et al 2002a;German et al 2004). The fourth one, LeFRK4, is expressed only in stamens (German et al 2002). The intracellular locations and the speciWc roles of each of these FRK isozymes are still unknown.…”

Section: Introductionmentioning

confidence: 99%

Evidence for intracellular spatial separation of hexokinases and fructokinases in tomato plants

Damari-Weissler

Kandel-Kfir

Gidoni

et al. 2006

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Four hexokinase (LeHXK1-4) and four fructokinase (LeFRK1-4) genes were identified in tomato plants. Previous GFP fusion studies indicate that the gene product of LeHXK3 is associated with the mitochondria while that of LeHXK4 is located within plastids. In this study we found that the enzyme encoded by the fructokinase gene LeFRK3 is also located within plastids. The presence of LeFrk3 enzyme in plastids raises the question of the origin of fructose in these organelles. The other three FRKs enzymes, LeFrk1&2&4, are located in the cytosol. Unlike LeFrk1&2&4, the two additional HXKs, LeHxk1&2, share a common membrane anchor domain and are associated with the mitochondria similar to LeHxk3. The difference in the locations of the cytoplasmic FRK and HXK isozymes suggests that glucose phosphorylation is confined to defined special intracellular localizations while fructose phosphorylation is less confined.