Comparison of RNA expression profiles between the two generations of Porphyra yezoensis (Rhodophyta), based on expressed sequence tag frequency analysis

To identify gene candidates related to the morphological and physiological differences between the gametophytic and sporophytic generations of a marine red alga, Porphyra yezoensis Ueda, large-scale expressed sequence tag (EST) analysis was conducted. A total of 10,625 5/-end EST sequences was generated from the sporophyte cDNA library, in addition to the previously published 10,154 ESTs from the gametophyte. A total of 20,779 ESTs was clustered into 4496 nonredundant groups at the criterion of 95% identity for 50 bases. Among the EST groups, only 1013 (22.5%) groups were classified as ESTs that commonly occurred in both generations, whereas a large proportion of EST groups were identified as being unique to either the gametophyte (1940 EST groups = 43.1%) or the sporophyte (1543 EST groups = 34.3%). A statistical significance test revealed 89 and 112 highly expressed gene candidates in the gametophyte and the sporophyte, respectively. Twelve candidate genes were subjected to RT-PCR analysis, and the differential expression was confirmed. Generation-specific regulation of alternative splicing of a transcript was demonstrated by RT-PCR analyses.