The evolution of fraction i protein during the origin of a new species of Nicotiana

Genetic attenuation of alkaloids and nicotine content in tobacco (Nicotiana tabacum)

MAIN CONCLUSION

The role of six alkaloid biosynthesis genes in the process of nicotine accumulation in tobacco was investigated. Downregulation of ornithine decarboxylase, arginine decarboxylase, and aspartate oxidase resulted in viable plants with a significantly lower nicotine content. Attenuation of nicotine accumulation in Nicotiana tabacum was addressed upon the application of RNAi technologies. The approach entailed a downregulation in the expression of six different alkaloid biosynthesis genes encoding upstream enzymes that are thought to function in the pathway of alkaloid and nicotine biosynthesis. Nine different RNAi constructs were designed to lower the expression level of the genes that encode the enzymes arginine decarboxylase, agmatine deiminase, aspartate oxidase, arginase, ornithine decarboxylase, and SAM synthase. Agrobacterium-based transformation of tobacco leaves was applied, and upon kanamycin selection, T0 and subsequently T1 generation seeds were produced. Mature T1 plants in the greenhouse were topped to prevent flowering and leaf nos. 3 and 4 below the topping point were tested for transcript levels and product accumulation. Down-regulation in arginine decarboxylase, aspartate oxidase, and ornithine decarboxylase consistently resulted in lower levels of nicotine in the leaves of the corresponding plants. Transformants with the aspartate oxidase RNAi construct showed the lowest nicotine level in the leaves, which varied from below the limit of quantification (20 μg per g dry leaf weight) to 1.3 mg per g dry leaf weight. The amount of putrescine, the main polyamine related to nicotine biosynthesis, showed a qualitative correlation with the nicotine content in the arginine decarboxylase and ornithine decarboxylase RNAi-expressing transformants. A putative early senescence phenotype and lower viability of the older leaves was observed in some of the transformant lines. The results are discussed in terms of the role of the above-mentioned genes in the alkaloid biosynthetic pathway and may serve to guide efforts to attenuate nicotine content in tobacco leaves.

Differential expression of ribulose-1,5-bisphosphate carboxylase in reciprocal F1 hybrids of a C3 and a C4-like Flaveria species

Stable reciprocal hybrids between Flaveria pringlei (C3) and F. brownii (C4-like) have been produced by standard breeding techniques. There are no differences in the isoelectric focusing patterns of the catalytic subunits of the ribulose-1,5-bisphosphate carboxylase/oxygenase from F. pringlei, F. brownii, or the reciprocal hybrids. The enzyme from both species also contains an identical noncatalytic subunit polypeptide. However, the carboxylase enzyme from F. brownii contains another isomeric form of noncatalytic subunit polypeptide which is resolveable by isoelectric focusing. This isomeric form constitutes about 50% of the total noncatalytic subunits in this species. It comprises only about 10% of the total noncatalytic subunit population in the C3 x C4 plants, but about 42% of the noncatalytic subunits in the reciprocal cross. The concentrations of the holoenzyme in the reciprocal hybrids are comparable to those of the respective maternal parent. We hypothesize that a differential inheritance of parental chloroplasts by the reciprocal hybrids may be associated with this apparent maternal influence on the expression of the noncatalytic polypeptides and the holoenzyme concentration.

Two dimensional analysis of chloroplast proteins from normal and cytoplasmic male sterile Brassica napus

Stromal and thylakoid proteins isolated from normal (N) and cytoplasmic male sterile (cms) lines of Brassica napus have been compared using a two dimensional gel separation. It has been shown that: 1) stromal compartments of the two lines were very similar; 2) although there was extensive homology between protein maps of thylakoids isolated from the two lines, these could be distinguished by the spots corresponding to the β subunits of the coupling factor CF1 from the ATPase complex.

Polypeptide composition of fraction 1 protein of the somatic hybrid between Petunia parodii and Petunia parviflora

The analysis of the subunit polypeptide composition of Fraction 1 protein provides information on the expression of both chloroplast and nuclear genomes. Fraction 1 protein, isolated from leaves of the somatic hybrid plants derived form the fusion of protoplasts of Petunia parodii and P. parviflora, was analyzed for its subunit polypeptide composition by isoelectric focusing in 8 M urea. The fraction 1 protein enzyme oligomer in the somatic hybrid plants contained small subunits resulting from the expression of both parental nuclear genomes, but probably only one of the parental large subunits, namely that of P. parodii. The relevance of such somatic hybrid material for the study of nucleocytoplasmic interrelationship is discussed, as well as the use of these fraction 1 protein isoelectric focusing patterns for the analysis of taxonomic relationships in Petunia.

Nicotiana Chromosome Coding for a Specific Polypeptide of the Small Subunit of Fraction 1 Protein

Fraction 1 protein has been isolated from leaves of a male sterile Nicotiana tabacum plant containing an extra N. debneyichromosome. The extra chromosome induces appearance of a third polypeptide composing the small subunit of fraction 1 protein, which otherwise contains two polypeptides as is shown by analysis of numerous different cultivars of N. tabacum.

Evolution of fraction 1 protein in the genus Lycopersicon

The large- and small-subunit polypeptide composition of fraction 1 protein contained in seven species of Lycopersicon and Solanum pennellii was determined by electrofocusing. The eight species of protein had large subunits composed of three polypeptides separated by about 0.05 pH unit, but there was no difference in the isoelectric points of the clusters of three polypeptides. By this criterion, no surviving mutations have appeared in the extranuclear DNA coding for the cluster of large-subunit polypeptides during a period of evolution which generated the eight species of plants. The genus Lycopersicon appears to be much younger than its sister genus Nicotiana in the family Solanaceae, where four types of polypeptide clusters have evolved. Three different small-subunit polypeptides whose isoelectric points are coded by nuclear DNA have arisen among the seven Lycopersicon species, and L. hirsutum and S. pennellii have proteins containing single polypeptides and are therefore considered older than L. chilense, L. chimielewskii, and L. parviflorum, whose proteins contain two polypeptides. L. cheesemanii, L. pimpinellifolium, and L. esculentum (and probably L. peruvianum) seem to be the most recently evolved species since their fraction 1 proteins have small subunits composed of three polypeptides.