ANALYSIS OF THE EXPRESSION OF 2 THIOLPROTEASE GENES FROM DAYLILY (HEMEROCALLIS SPP.) DURING FLOWER SENESCENCE

A cDNA clone encoding a daylily (Hemerocallis spp.) thiolprotease (SEN 11), whose expression is strongly upregulated in flower tepal senescen ce, has been isolated. The amino acid sequence, deduced from the nucle otide sequence, showed highest similarity to plant thiolproteases of V igna mungo, Phaseolus vulgaris and Hemerocallis (SEN102), and contains a putative ER retention signal that has been described in Vigna mungo . SEN102 and SEN11 transcripts were not detectable in flower buds at t he opening stage, but two peaks of transcripts were seen after 9 h and 19 h, in both petals and sepals, when wilting symptoms were apparent. The pattern of protease activity migrating on a 26.3 kDa protein was similar to the SEN102 and SEN11 transcript profiles. These two genes w ere also expressed in stamens and leaves, but their transcripts were u ndetectable in carpels and rhizomes. The expression of SEN102 was lowe r in the senescent leaf than in the green leaf. The pattern of express ion of these genes suggests their involvement in the protein hydrolysi s occurring in tepals at the late senescence stage, whereas in leaves they could be involved in the constitutive protein turnover machinery. Exogenous gibberellic acid application to cut flowers increased trans cripts of both genes.