The possible role of PnACS2 in IAA-mediated flower inhibition in Pharbitis nil

In this work we studied interactions between auxin and ethylene in the inhibition of photoperiodic flower induction in SDP Pharbitis nil. To this end, PnACS2 was cloned and its expression was studied under various photoperiodic conditions, as well as under the influence of auxin. The full-length PnACS2 cDNA consists of 1,841 bp and encodes for 472 amino acids, with the 80-bp 5'- and the 417-bp 3'-untranslated regions. It was shown that the gene is transcribed in all organs of 5-day-old seedlings and that it is strongly activated by auxin. The maximal transcriptional activity of PnACS2 and the strongest stimulation of its activity by IAA occur in the cotyledons. This confirms the speculation that the inhibitory effect of auxin on P. nil flowering results from its stimulatory effect on ethylene production.