CLONING AND SEQUENCE OF A CDNA-ENCODING A NOVEL HYBRID PROLINE-RICH PROTEIN ASSOCIATED WITH CYTOKININ-INDUCED HAUSTORIA FORMATION IN CUSCUTA-REFLEXA

A complete cDNA encoding a novel hybrid Pro-rich protein (HyPRP) was i dentified by differentially screening 3x10(4) recombinant plaques of a Cuscuta reflexa cytokinin-induced haustorial cDNA library constructed in lambda gt10. The nucleotide (nt) sequence consists of: (i) a 424-b p 5'-non coding region having five start codons (ATGs) and three upstr eam open reading frames (uORFs); (ii) an ORF of 987 bp with coding pot ential for a 329-amino-acid (aa) protein of M(r), 35203 with a hydroph obic N-terminal region including a stretch of nine consecutive Phe fol lowed by a Pro-rich sequence and a Cys-rich hydrophobic C terminus; an d (iii) a 178-bp 3'-UTR (untranslated region). Comparison of the predi cted aa sequence with the NBRF and SWISSPROT databases and with a rece nt report of an embryo-specific protein of maize [Jose-Estanyol et al. , Plant Cell 4 (1992) 413-423] showed it to be similar to the class of HyPRPs encoded by genes preferentially expressed in young tomato frui ts, maize embryos and in vitro-cultured carrot embryos. Northern analy sis revealed an approx. 1.8-kb mRNA of this gene expressed in the suba pical region of the C. reflexa vine which exhibited maximum sensitivit y to cytokinin in haustorial induction.