HEXOKINASE AS A SUGAR SENSOR IN HIGHER-PLANTS

The mechanisms by which higher plants recognize and respond to sugars are largely unknown. Here, we present evidence that the first enzyme i n the hexose assimilation pathway, hexokinase (HXK), acts as a sensor for plant sugar responses. Transgenic Arabidopsis plants expressing an tisense hexokinase (AtHXK) genes are sugar hyposensitive, whereas plan ts overexpressing AtHXK are sugar hypersensitive. The transgenic plant s exhibited a wide spectrum of altered sugar responses in seedling dev elopment and in gene activation and repression. Furthermore, overexpre ssing the yeast sugar sensor YHXK2 caused a dominant negative effect b y elevating HXK catalytic activity but reducing sugar sensitivity in t ransgenic plants. The result suggests that HXK is a dual-function enzy me with a distinct regulatory function not interchangeable between pla nts and yeast.