Molecular genetic analysis of left–right handedness in plants

Abstract

Handedness in plant growth may be most familiar to us when we think of tendrils or twining plants, which generally form consistent right– or left–handed helices as they climb. The petals of several species are sometimes arranged like fan blades that twist in the same direction. Another less conspicuous example is ‘circumnutation’, the oscillating growth of axial organs, which alternates between a clockwise and an anti–clockwise direction. To unravel molecular components and cellular determinants of handedness, we screenedArabidopsis thalianaseedlings for helical growth mutants with fixed handedness. Recessivespiral1andspiral2mutants show right–handed helical growth in roots, hypocotyls, petioles and petals; semi–dominantlefty1andlefty2mutants show opposite left–handed growth in these organs.leftymutations are epistatic tospiralmutations.Arabidopsishelical growth mutants with fixed handedness may be impaired in certain aspects of cortical microtubule functions, and characterization of the mutated genes should lead us to a better understanding of how microtubules function in left–right handedness in plants.