A TRANSMITTING TISSUE-XPRESSED AND POLLEN-EXPRESSED PROTEIN FROM SUNFLOWER WITH SEQUENCE SIMILARITY TO THE HUMAN RTP PROTEIN

A novel pistil-and pollen-expressed gene (sf21) encoding a 352 amino a cid long polypeptide was isolated by differential screening of a flora l 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 h omology with an unidentified polypeptide from human cerebellum (N-term inus) and with the ligand binding region of the vertebrate inositol 1, 4,5 trisphosphate (IP3) receptor (C-terminus). The sf21 gene is expres sed in young and mature florets of an open inflorescence but not at th e 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 transcri pts towards the ovule, is observed during specific stages in tobacco p istils. The transcripts gradually disappear as the pollen tubes grow t hrough the transmitting tissue. These observations suggest that the pr otein acts in pollen-pistil interactions. (C) 1997 Elsevier Science Ir eland Ltd.