The biosynthetic pathway of cyclic carotenoid is known to be quantitatively and qualitatively different in the non-green plastids of Capsicum annuum fruits compared with chloroplasts. Here, the cloning is described of a novel cDNA from this organism, which encodes an enzyme catalyzing the cyclization of lycopene to beta-carotene when expressed in Escherichia coli. The corresponding gene is constitutively expressed during fruit development. Significant amino acid sequence identity was observed between this enzyme and capsanthin/capsorubin synthase which is involved in the synthesis of the species-specific red carotenoids of C. annuum fruits. The latter enzyme was found also to possess a lycopene beta-cyclase activity when expressed in E. coli. A model is proposed for the origin of the capsanthin/capsorubin synthase gene and the role of this enzyme, together with the newly cloned lycopene cyclase, in the specific re-channeling of linear carotenoids into beta-cyclic carotenoids in C. annuum ripening fruits.

~bstract We have cloned a cDNA from the plant Capsicum annuum which encodes a novel enzyme mediating the dehydrogenation of ~-carotene and neurosporene to lycopene when expressed in E. coli cells accumulating ~-carotene or neurosporene. this enzyme is unable to dehydrogenate either phytoene or lycopene. The deduced amino acid sequence suggests that this cDNA encodes a polypeptide whose mature size is ca. 59 kDa and which is synthesized as a precursor with a NH2-terminal extension resembling transit peptides for plastid targeting. Sequence comparison reveals 33-35% similarity with previously cloned plant or cyanobacterial phytoene desaturases. In contrast, only limited sequence similarity is found with a ~-carotene desaturase from the cyanobacterium Anabaena.

The c‐abl gene encodes a protein tyrosine kinase and is transcribed from at least two promoters giving rise to transcripts of two size classes of approximately 5 and 6 kb in length. These mRNAs only differ in their most 5′ exon and encode proteins of similar size but with different N‐termini. In the mouse testis an additional abundant c‐abl mRNA of 4 kb is detected. This mRNA was shown to be expressed in the haploid male germ cells of the adult mouse. Here we describe the cloning and molecular characterization of a cDNA representing the testis specific c‐abl transcript. We show that the 4 kb c‐abl mRNA arises from alternative polyadenylation of an RNA transcribed from the same promoter as the 5 kb mRNA. The site of polyadenylation is unusual in this shorter transcript as it is not preceded by the highly conserved hexanucleotide AAUAAA. The use of this polyadenylation site removes 1.2 kb of 3′ sequences present in the somatic c‐abl mRNAs, but does not affect the main open reading frame of the transcript. Using in situ hybridization on whole testis sections it is shown that the 4 kb c‐abl mRNA is most abundant in the elongating spermatids.

SummaryA 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 lightand 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.