Abstract
We have investigated the molecular genetic mechanism of gravitropism of Arabidopsis inflorescence stems. We have demonstrated that vacuoles, which are multi-functional and characteristic organelle of plant cell, have higher-ordered novel function for gravity sensing. Gravity stimuli are perceived as amyloplasts movement toward the direction of gravity in the endodermal cell. Functions and membrane dynamics of vacuoles are closely related to the amyloplasts movement. To elucidate genetic network involved in the organelle dynamics, we have performed molecular genetic studies of several genes important for shoot gravitropism listed below; Qb-SNARE ZIG/SGR4/VTI11 and Qa-SNARE SGR3/SYP22 involved in vesicular transport between the trans-Golgi network and vacuoles, phospholipase A1-like SGR2 localized to vacuoles and dot-like organelle, and SGR8 homologous to C. elegans Rme-8 (Receptor-mediated endocytosis-8). We will report the genetic characterization for suppressor genes of zig and sgr2 mutants. Involvement of these genes in vacuolar membrane dynamics in the endodermal cells will be discussed.
