THE PLANT CELL, Vol 5, Issue 11 1513-1528, Copyright © 1993 by American Society of Plant Biologists
Immunolocalization of the G Protein [alpha] Subunit Encoded by the GPA1 Gene in Arabidopsis
C. A. Weiss, H. Huang and H. Ma
Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724-2212
Heterotrimeric GTP binding proteins (G proteins) are important signal
transducers in lower eukaryotes and in animal cells. In plants, the
occurrence of GTP binding proteins has been reported, but their biological
function remains unclear. Two genes coding for G protein [alpha] subunits
have been cloned: GPA1 in Arabidopsis and TGA1 in tomato. To gain some
insights into the function of GPA1, we describe an extensive
immunolocalization of GP[alpha]1, the gene product of GPA1, during
Arabidopsis development. Our results show that GP[alpha]1 is present
through all stages of development and in all organs examined, with the
exception of mature seeds. It is expressed in roots, floral stem, rosette
leaves, cauline leaves, flowers, and seedpods. Interestingly, the level of
GP[alpha]1 protein is higher in immature organs than in mature organs.
GP[alpha]1 is present at a high level in the root meristem and elongation
zone, in the shoot and floral meristems, and in the leaf primordium and
floral organ (sepal, petal, stamen, and gynoecium) primordia. During flower
development, dividing microspores, but not mature pollen, show high levels
of GP[alpha]1. During pollination, GP[alpha]1 is present in the growing
pollen tubes. The protein is also present in nectaries and developing
ovules and, after fertilization, in developing embryos. In mature tissue,
GP[alpha]1 is preferentially found in the vascular system but is also
present in other cell types. The complexity of the GP[alpha]1 localization
pattern suggests that GP[alpha]1 might be involved in different signaling
pathways depending on the developmental stage.
