PROMOTER ANALYSIS AND EXPRESSION OF A PHOSPHOLIPASE-D GENE FROM CASTOR BEAN

The expression of a castor bean (Ricinus commonis L.) phospholipase D (PLD; EC 3.1.4.4) gene has been studied by examining its promoter acti vity in transgenic tobacco (Nicotiana tabacum) carrying a PLD promoter -glucuronidase transgene and by monitoring the levels of PLD mRNA in c astor bean. Sequence and the 5' truncation analyses revealed that the 5' flanking region from nucleotide -1200 to -730 is required for the r egulation and basal function of the PLD promoter. The PLD promoter in vegetative tissues is highly active in the rapidly growing regions suc h as the shoot apex and the secondary meristem producing axillary buds and vascular tissues of young leaves and stems. The PLD promoter acti vity in floral tissues was high in stigma, ovary, and pollen grains, b ut low in petals, sepals, the epidermis of anthers, styles, and filame nts. The PLD promoter activity was enhanced by abscisic acid. Northern -blot analysis of PLD in castor bean showed that the PLD mRNA levels w ere high in young and metabolically more active tissues such as expand ing leaves, hypocotyl hooks, developing seeds, and young seedlings, an d they decreased in mature tissues such as fully expanded leaves and d eveloped seeds. These patterns of expression suggest a role of PLD in rapid cell growth, proliferation, and reproduction.