Drought- 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 fibrillin (fib) gene, along with two carotenoid biosynthesis genes, namely those encoding geranylgeranyl pyrophosphate synthase (ggpps) and capsanthin-capsorubin synthase (ccs) from bell pepper (Capsicum annuum), whose expression is greatly induced during fruit ripening. A homologous transient expression assay has shown that high expression of these genes in pepper fruit is regulated essentially at the transcriptional level. Transcription of ccs is mainly fruit-specific and that of ggpps is highly induced in fruits. Expression of fib is more complex: it is induced not only by a developmental process in fruits but also, in pepper and tobacco leaves, by diverse environmental factors such as drought and mechanical wounding. The wound-induced transcriptional activation of fib is light- and oxygen-dependent. Evidence is provided for the involvement of superoxide anion production within plastids in the signalling pathway leading to induction of this nuclear gene by environmental stresses. Specific activation of this promoter in roots, but not in leaves, was also observed upon exogenous abscisic acid treatment. Drought or wounding also leads to the accumulation of the fibrillin polypeptide in leaves. Furthermore, a low level of fibrillin has also been detected in the leaves of nonstressed plants. Taken together, our data suggest a general role for fibrillin in various plastid types and in response to environmental stresses, in addition to its function in assembly of carotenoid-containing fibrils in chromoplasts.