Functional analysis of G-proteins has been extensively carried out using their over-expressing lines and knockout mutants in plants. Since α subunit exists in an active or inactive form, overexpressing α subunit does not mean that G-protein signaling pathways are activated in the transgenic lines. Ectopic expression of the constitutively active form of the α subunit will magnify a role of G-protein signaling pathways in plant growth and development, and ultimately yield phenotypes. Here, we describe the method to study function of G-proteins in chloroplast development using the constitutively active form of the α subunit in Arabidopsis.