Plant Physiol, July 2002, Vol. 129, pp. 1119-1126
Distinct Physiological Roles of Fructokinase Isozymes Revealed by
Gene-Specific Suppression of Frk1 and Frk2
Expression in Tomato
Saori
Odanaka,
Alan B.
Bennett, and
Yoshinori
Kanayama*
Faculty of Agriculture, Tohoku University, Aoba-ku, Sendai
981-8555, Japan (S.O., Y.K.); and Mann Laboratory, University of
California, Davis, California 95616 (A.B.B., Y.K.)
There are two divergent fructokinase isozymes, Frk1 and Frk2 in
tomato (Lycopersicon esculentum Mill.) plants. To
investigate the physiological functions of each isozyme, the expression
of each fructokinase mRNA was independently suppressed in transgenic tomato plants, and the respective phenotypes were evaluated.
Suppression of Frk1 expression resulted in delayed
flowering at the first inflorescence. Suppression of
Frk2 did not effect flowering time but resulted in
growth inhibition of stems and roots, reduction of flower and fruit
number, and reduction of seed number per fruit. Localization of
Frk1 and Frk2 mRNA accumulation by in
situ hybridization in wild-type tomato fruit tissue indicated that
Frk2 is expressed specifically in early tomato seed
development. Fruit hexose and starch content were not effected by the
suppression of either Frk gene alone. The results
collectively indicate that flowering time is specifically promoted by
Frk1 and that Frk2 plays specific roles in contributing to stem and
root growth and to seed development. Because Frk1 and
Frk2 gene expression was suppressed individually in
transgenic plants, other significant metabolic roles of fructokinases may not have been observed if Frk1 and Frk2 play, at least partially, redundant metabolic roles.
*
Corresponding author; e-mail kanayama{at}bios.tohoku.ac.jp; fax
81-22-717-8642.
© 2002 American Society of Plant Physiologists
