ISOLATION AND CHARACTERIZATION OF PHASE-SPECIFIC COMPLEMENTARY DNAS FROM SPOROPHYTES AND GAMETOPHYTES OF PORPHYRA-PURPUREA (RHODOPHYTA) USING SUBTRACTED COMPLEMENTARY-DNA LIBRARIES

The red alga Porphyra purpurea (Roth) C. Agardh has a life cycle that alternates between shell-boring, filamentous sporophytes and free-livi ng, foliose gametophytes. The significant morphological differences be tween these two phases suggest that many genes should be developmental ly regulated and expressed in a phnse-specific manner. In this study, we prepared and screened subtracted complementary DIVA (cDNA) librarie s specific for the sporophyte and gametophyte of P. purpurea. This inv olved the construction of cDNA libraries from each phase, followed by the removal of common clones through subtractive hybridization. Sampli ng of the subtracted libraries indicated that 8-10% of the recombinant colonies in each library were specific for the appropriate phase. Of 20 putative phase-specific cDNAs selected from each subtracted library , eight unique clones were obtained for the sporophyte and seven for t he gametophyte. After confirming their phase-specificities by hybridiz ation to gametophyte and sporophyte messenger RNA, these 15 phase-spec ific cDNAs were sequenced, and the deduced amino acid sequences were u sed to search protein databanks. Two proteins encoded by the sporophyt e-specific cDNAs and two by the gametophyte-specific cDNAs were identi fied by their similarity to databank entries.