Isolation and characterization of a cDNA encoding a sar-like monomeric GTP-binding protein in Avena fatua L.

Differential display of mRNAs from embryos of Avena fatua L. caryopses was used to isolate an mRNA more abundant in nondormant than dormant caryopses during early imbibition. The DNA sequence of the corresponding 579 bp cDNA, termed Af SAR1, is 92% identical to an Arabidopsis cDNA encoding the monomeric GTP-binding protein sar1p. Predicted amino acid sequences of the four conserved CTP binding and hydrolysis domains in Af SAR1 are 100% identical to sar1p. Af SAR1 mRNA levels increased 6-fold or more than 10-fold in nondormant embryos during the first 48 h of imbibition in water or GA(3), respectively. However, mRNA levels increased only slightly and transiently in dormant embryos imbibed in water, mRNA abundance was highest in meristematic and actively growing tissues of A. fatua seedlings. Af SAR1 belongs to a small (two to four members) gene family as judged by Southern hybridizations. Increased abundance of this mRNA during early germination and in actively growing tissues indicates that the respective protein is associated with rapid cell elongation, cell division and growth. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.