A glucuronokinase gene in Arabidopsis, AtGlcAK, is involved in drought tolerance by modulating sugar metabolism

Arabidopsis glucuronokinase (AtGlcAK), as a member of the GHMP kinases family, is implicated in the de novo synthesis of UDP-glucuronic acid (UDP-GlcA) by the myo-inositol oxygenation pathway. In this study, two T-DNA insertion homozygous mutants of AtGlcAK, atglcak-1 and atglcak-2, were identified. AtGlcAK was highly expressed in roots and flowers. There was reduced primary root elongation and lateral root formation in atglcak mutants under osmotic stress. The atglcak mutants displayed enhanced stomatal opening in response to abscisic acid (ABA), elevated water loss and impaired drought tolerance. Under water stress, the accumulation of reducing and soluble sugars was reduced in atglcak mutants, and the metabolism of glucose and sucrose was affected by the synthetic pathway of UDP-GlcA. Furthermore, a reduced level of starch in atglcak mutants was observed under normal conditions. The phylogenetic analysis suggested that GlcAK was conserved in numerous dicots and monocots plants. In short, AtGlcAK mutants displayed hypersensitivity to ABA and reduced root development under water stress, rendering the plants more susceptible to drought stress.