MOLECULAR ANALYSIS OF TRI-MUTANT ALLELES IN TOMATO INDICATES THE TRI LOCUS IS THE GENE ENCODING THE APOPROTEIN OF PHYTOCHROME B1

Four monogenic recessive tomato (Lycopersicon esculentum Mill.) mutant s at the temporarily red light-insensitive (tri) locus (tri(1), tri(2) in the genetic background breeding line GT; tri(3), tri(4) in the gen etic background cultivar Moneymaker) were studied. These mutants had s lightly longer hypocotyls under white light than the wild type (WT). W estern-blot analysis showed that the tri(1) mutant was deficient in a relatively light-stable phytochrome apoprotein (116 kDa) that was reco gnized in the WT by an antibody to tobacco phytochrome B; tri(2) had a 166-kDa band reduced in abundance; and tri(2) and tri(4) had bands re duced in molecular mass, approx. 105 and 95 kDa, respectively. These p atterns were also found in light-grown plants. Northern-blot analysis for PHYB1 mRNA showed for tri(2) a transcript approx. 2 kb larger, for tri(4), a transcript of WT size, but much reduced in abundance and fo r a tri(1) and tri(3) transcripts equivalent in size and abundance to WT, In these mutants the transcripts of other members of the tomato ph ytochrome gene family (PHYA, PHYB2, PHYE, PHYF) were indistinguishable in size and abundance from WT, Thus, it appears that the Tri locus sp ecifically affects PHYB1 gene expression. Unlike phytochrome-B mutants in other plants, de-etiolated seedlings of the tri mutants exhibited normal responses to end-of-day far-red (EODFR) light and supplementary far-red light during the day. Since the holophytochromes of types B1 and B2 (phyB1 and phyB2) are closely related, it is proposed that ther e might be redundancy between them for these responses.