The promoter region of the Zinnia elegans basic peroxidase isoenzyme gene contains cis-elements responsive to nitric oxide and hydrogen peroxide

NO and H₂O₂ are important biological messengers in plants. They are formed during xylem differentiation in Zinnia elegans and apparently play important roles during the xylogenesis. To ascertain the responsiveness of the Z. elegans peroxidase (ZePrx) to these endogenous signals, the effects of NO and H₂O₂ on ZePrx were studied. The results showed that ZePrx is up-regulated by NO and H₂O₂, as confirmed by RT-qPCR, and that its promoter contains multiple copies of all the putative ris-elements (ACGT box, OCS box, OPAQ box, L1BX, MYCL box and W box) known to confer regulation by NO and H₂O₂. Like other OCS elements, the OCS element of ZePrx contains the sequence TACG that is recognized by OBF5, a highly conserved bZIP transcription factor, and the 10 bp sequence, ACAaTTTTGG, which is recognized by OBP1, a Dof domain protein that binds down-stream the OCS element. Furthermore, the ZePrx OCS element is flanked by two CCAAT-like boxes, and encloses one auxin-responsive ARFAT element and two GA₃-responsive Pyr boxes. Results also showed that ZePrx may be described as the first protein to be up-regulated by NO and H₂O₂, whose mRNA contains several short-longevity conferring elements, such as a downstream (DST) sequence analogous to the DSTs contained in the highly unstable SAUR transcripts. The presence of these regulatory elements strongly suggests that ZePrx is finely regulated, as one may expect from an enzyme that catalyzes the last irreversible step of the formation of lignins, the major irreversible sink for the photosynthetically fixed CO₂.