PLANT BIOLOGY Sugar Signaling Between Plasma and Plastid Membranes

D-glucose is a nutrient produced and used by plants. However, high concentrations of glucose inhibit root growth. The single G protein subunit (GPA1) in Arabidopsis thaliana has been implicated in inhibition of glucose-mediated root growth. gpa1-null plants are hypersensitive to glucose-mediated inhibition of root growth, and plants expressing a constitutively active form of GPA1 are resistant to such growth inhibition. Huang et al. identified THYLAKOID FORMATION 1 (THF1) as an interacting partner for GPA1 in a yeast two-hybrid assay and confirmed this interaction in vitro and by coimmunoprecipitation from Arabidopsis suspension cells transfected with a tagged form of THF1. THF1 was localized to the plastid outer membrane and the stromules, which are extensions of the plastids that are enclosed in both the inner and outer plastid envelope. Förster resonance energy transfer (FRET) demonstrated that THF1 and GPA1 physically interacted at sites where the plastid membrane was adjacent to the plasma membrane. Plants deficient in THF1 exhibited even shorter roots under high-glucose conditions than did the GPA1-deficient plants, and the roots of plants overexpressing THF1 grew faster under all glucose conditions than did wild-type plant roots. Epistasis analysis placed THF1 downstream of GPA1 in the glucose signaling pathway. Exposure to elevated glucose caused a decrease in THF1 abundance in roots, whereas there was no change in THF1 abundance in leaves. Thus, GPA1 and THF1 appear to link the plasma membrane and plastid membrane to mediate signals involved in responses to changes in glucose concentration.

J. Huang, J. P. Taylor, J.-G. Chen, J. F. Uhrig, D. J. Schnell, T. Nakagawa, K. L. Korth, A. M. Jones, The plastid protein THYLAKOID FORMATION1 and the plasma membrane G-protein GPA1 interact in a novel sugar-signaling mechanism in Arabidopsis. Plant Cell 18, 1226-1238 (2006). [Abstract] [Full Text]