Constitutively overexpressing a tomato fructokinase gene (LeFRK1) in cotton (Gossypium hirsutum L. cv. Coker 312) positively affects plant vegetative growth, boll number and seed cotton yield

Abstract

Increasing fructokinase (FRK) activity in cotton (Gossypium hirsutum L.) plants may reduce fructose inhibition of sucrose synthase (Sus) and lead to improved fibre yield and quality. Cotton was transformed with a tomato (Solanum lycopersicum L.) fructokinase gene (LeFRK1) under the control of the CMV 35S promoter. In a greenhouse, the LeFRK1 plants had increased fibre and leaf FRK activity over nonexpressing nulls, but not improved fibre length and strength. Compared with the nulls, LeFRK1 plants yielded 13–100% more seed-cotton mass per boll and more bolls per plant, and therefore more seed cotton and fibre yield per plant. The enhanced yield was related to a greater seed number per boll for LeFRK1 plants. Photosynthetic rates were not appreciably different among genotypes. However, more area per leaf and leaf number (in some instances) for LeFRK1 plants than for nulls enhanced the capacity for C gain. Larger leaf areas for LeFRK1 plants were associated with larger stem diameters. Lower sucrose levels in developing leaves of LeFRK1 plants suggest that LeFRK1 overexpression leads to improved in vivo Sus activity in developing leaves and possibly in developing seeds. The improvement in yield for LeFRK1 plants may also be the result of improvements in photosynthate supply as a consequence of greater leaf area.

Increased activity of MdFRK2, a high-affinity fructokinase, leads to upregulation of sorbitol metabolism and downregulation of sucrose metabolism in apple leaves

“…As we had expected, elevated FRK activity significantly decreased the fructose concentrations in mature leaves, similar to the connection between diminished FRK expression and higher fructose levels in potato 21 and aspen 19 . Transgenic cotton plants that overexpressed tomato LeFRK1 have significantly increased FRK enzyme activity; however, fructose concentrations are unchanged in the leaves of homozygous T3 plants 23 . Km values are higher for LeFRK1 (1300 µm) than those for LeFRK2 (54–220 µm), and almost no enzyme activity occurs under low-fructose conditions in yeast systems 11 .…”

“…However, in transgenic aspen, the reduction of FRK activity by using an RNAi- FRK2 approach increased the leaf concentrations of fructose, glucose, and sucrose but decreased cell wall fiber thickness and the proportion of cellulose in the cell wall, implying that FRK2 is required for carbon partitioning to cellulose in the wood 19 . Additionally, overexpression of tomato low-affinity LeFRK1 in cotton ( Gossypium hirsutum ) results in a decreased level of sucrose in young leaves but increases in seed and fiber yields per plant due to the increased area per leaf and leaf number 23 . Although the physiological roles of FRK in plant development have been partly elucidated in these plant species, the underlying function of FRK in regulating carbohydrate concentrations remains obscure, and no studies have investigated the impacts of enhanced high-affinity FRK activity on sugar metabolism and plant growth.…”

Plant Fructokinases: Evolutionary, Developmental, and Metabolic Aspects in Sink Tissues

“…Overexpression of potato FRK ( StFK ) in potato and tomato plants did not reveal any significant beneficial effects ( German et al, 2003 ; Davies et al, 2005 ). On the other hand, overexpression of tomato SlFRK1 in cotton ( Gossypium hirsutum ) increased the number of cotton bolls per plant, the number of seeds per boll, and fiber mass per plant, without affecting fiber length or fiber strength ( Mukherjee et al, 2015 ). It has been suggested that these phenotypes result from the increased leaf area of the SlFRK1 -overexpressing plants at the time of flowering, which allows for greater carbon assimilation per plant ( Mukherjee et al, 2015 ).…”

“…On the other hand, overexpression of tomato SlFRK1 in cotton ( Gossypium hirsutum ) increased the number of cotton bolls per plant, the number of seeds per boll, and fiber mass per plant, without affecting fiber length or fiber strength ( Mukherjee et al, 2015 ). It has been suggested that these phenotypes result from the increased leaf area of the SlFRK1 -overexpressing plants at the time of flowering, which allows for greater carbon assimilation per plant ( Mukherjee et al, 2015 ). Further research is required to demonstrate any positive effects of FRK overexpression, possibly in a tissue-specific manner and perhaps together with SUS, as it has been suggested that FRKs and SUS may work in concert to regulate sucrose metabolism ( Davies et al, 2005 ).…”

Sugar Metabolism and Fruit Development in the Tomato

“…The first of these targeted fructokinase (FRK), which is essential for fructose metabolism following the production of fructose and hexose from sucrose that has been unloaded into fruit cells. FRK is known to be the major enzyme involved in phosphorylating fructose to fructose-6-phosphate, which is utilized in starch biosynthesis, and plants contain several FRK genes with different expression patterns and physiological roles (Granot et al, 2014;Kanayama et al, 1997;Mukherjee et al, 2015). Thus, FRK gene expression has been suppressed in an attempt to increase the fructose concentration in tomato fruit (Odanaka et al, 2002).…”