Suppression of fructokinase encoded by LeFRK2 in tomato stem inhibits growth and causes wilting of young leaves

Abstract

These authors equally contributed to this work. SummaryFructokinases catalyze the key step of fructose phosphorylation in plants. LeFRK2, the major fructokinaseencoding gene in tomato plants, is abundantly expressed in roots, stems, and fruits. To analyze the role of LeFRK2 in plant development, we analyzed transgenic tomato plants with sense and antisense expression of StFRK, the potato homolog of LeFRK2. Increased fructokinase activity had no effect. However, plants in which LeFRK2 was speci®cally suppressed, either via antisense suppression or via co-suppression, exhibited growth inhibition and wilting of young leaves at daytime. Grafting experiments indicated that a stem interstock of antisense plants was suf®cient to inhibit growth and cause leaf wilting. Stem secondary xylem exhibited particular suppression of LeFRK2 and the area of active xylem, estimated by eosin uptake, was signi®cantly smaller in antisense stem compared to that of wild-type plants. These results suggest that LeFRK2 might be required for proper development of xylem that affected growth and wilting.

Tricarboxylic Acid Cycle Activity Regulates Tomato Root Growth via Effects on Secondary Cell Wall Production

“…While considerable research effort has been expended on defining the importance of nucleotide sugar precursors in the regulation of cell wall biosynthesis (Amor et al, 1995;Cronin and Hay, 1996;German et al, 2003;Reiter, 2008), relatively few studies have directly focused on the general role that primary metabolism, and more specifically energy metabolism, plays in this process. Our recurrent observations that tomato plants deficient in the expression of genes encoding enzymes of the mitochondrial TCA cycle exhibited stunted root growth (Carrari et al, 2003;Studart-Guimarães et al, 2007;van der Merwe et al, 2009) have driven us to address the question of whether cell wall biosynthesis is energy limited in roots.…”

“…However, many pathways and processes have been studied in isolation, and the relative importance of primary plant metabolism to the sustenance and regulation of either anabolic polymer production or secondary metabolism has received relatively scant attention. Indeed, publications directly addressing such questions are few and instead tend to concentrate on the direct (primary) precursors of specific pathways (Amor et al, 1995;Cronin and Hay, 1996;German et al, 2003;Ruan et al, 2003;Reiter, 2008). For example, coordination of primary metabolism and cell wall synthesis has largely focused on the immediate precursors, such as different nucleotide sugars (Amor et al, 1995;Ruan et al, 2003;Reiter, 2008).…”

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

“…Being aware of this effect, we also selected poorly growing kanamycin-resistant transformants, which appear to be those with high levels of AtHXK1 expression. Such a bias in the selection of transgenic plants may be present in many other cases, as we previously observed in an investigation of antisense suppression of LeFRK2 (German et al, 2003). Therefore, care should be taken to avoid discrimination against the most interesting transformants.…”

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

“…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).…”