Kruter-Canham_1997_Plant.Sci_129_191

A novel pistil- and pollen-expressed gene (sf21) encoding a 352 amino acid long polypeptide was isolated by differential screening of a floral cDNA library from sunflower (Helianthus annuus L.) and characterized. The deduced polypeptide is structurally related to the human protein RTP and the mouse protein Ndr1. It also shares significant sequence homology with an unidentified polypeptide from human cerebellum (N-terminus) and with the ligand binding region of the vertebrate inositol 1,4,5 trisphosphate (IP3) receptor (C-terminus). The sf21 gene is expressed in young and mature florets of an open inflorescence but not at the floral bud stage. In the sunflower pistil, expression is restricted to the transmitting tissue and the phloem cells. The same location of expression, with an increasing concentration gradient of SF21 transcripts towards the ovule, is observed during specific stages in tobacco pistils. The transcripts gradually disappear as the pollen tubes grow through the transmitting tissue. These observations suggest that the protein acts in pollen-pistil interactions.