DROUGHT-INDUCED AND WOUND-INDUCED EXPRESSION IN LEAVES OF A GENE ENCODING A CHROMOPLAST CAROTENOID-ASSOCIATED PROTEIN

A study has been carried out to investigate the regulation of the fibr illin (fib) gene, along with two carotenoid biosynthesis genes, namely those encoding geranylgeranyl pyrophosphate synthase (ggpps) and caps anthin-capsorubin synthase (ccs) from bell pepper (Capsicum annuum), w hose expression is greatly induced during fruit ripening. A homologous transient expression assay has shown that high expression of these ge nes in pepper fruit is regulated essentially at the transcriptional le vel. Transcription of ccs is mainly fruit-specific and that of ggpps i s highly induced in fruits. Expression of fib is more complex: it is i nduced not only by a developmental process in fruits but also, in pepp er and tobacco leaves, by diverse environmental factors such as drough t and mechanical wounding. The wound-induced transcriptional activatio n of fib is light- and oxygen-dependent. Evidence is provided for the involvement of superoxide anion production within plastids in the sign alling pathway leading to induction of this nuclear gene by environmen tal stresses. Specific activation of this promoter in roots, but not i n leaves, was also observed upon exogenous abscisic acid treatment. Dr ought or wounding also leads to the accumulation of the fibrillin poly peptide in leaves. Furthermore, a low level of fibrillin has also been detected in the leaves of nonstressed plants. Taken together, our dat a suggest a general role for fibrillin in various plastid types and in response to environmental stresses, in addition to its function in as sembly of carotenoid-containing fibrils in chromoplasts.