We used DNA sequencing and gel blot surveys to assess the integrity of the chloroplast gene infA , which codes for translation initiation factor 1, in Ͼ 300 diverse angiosperms. Whereas most angiosperms appear to contain an intact chloroplast infA gene, the gene has repeatedly become defunct in ‫ف‬ 24 separate lineages of angiosperms, including almost all rosid species. In four species in which chloroplast infA is defunct, transferred and expressed copies of the gene were found in the nucleus, complete with putative chloroplast transit peptide sequences. The transit peptide sequences of the nuclear infA genes from soybean and Arabidopsis were shown to be functional by their ability to target green fluorescent protein to chloroplasts in vivo. Phylogenetic analysis of infA sequences and assessment of transit peptide homology indicate that the four nuclear infA genes are probably derived from four independent gene transfers from chloroplast to nuclear DNA during angiosperm evolution. Considering this and the many separate losses of infA from chloroplast DNA, the gene has probably been transferred many more times, making infA by far the most mobile chloroplast gene known in plants. INTRODUCTIONMany genes have been lost from the chloroplast genome during plant and algal evolution. Most of these losses occurred in the murky interval between the original endosymbiosis of a cyanobacterium (with perhaps 2000 proteincoding genes) and the last common ancestor of all existing chloroplast genomes (with ‫ف‬ 210 protein-coding genes; . Many other genes were lost during the early evolution of photosynthetic eukaryotes, often in parallel in different algal lineages, and some of these losses were the result of gene transfers to the nuclear genome . During the evolution of land plants, relatively few changes occurred to the set of genes found in chloroplast DNA (cpDNA) Palmer and Delwiche, 1998). Nonetheless, the most recent changes are likely to provide the most information about the evolutionary mechanisms involved.Among the six completely sequenced chloroplast genomes from angiosperms (excluding the nonphotosynthetic plant Epifagus virginiana ; Wolfe et al., 1992a), 74 proteincoding genes are held in common and an additional five are present in only some species. These five genes are accD , ycf1 , and ycf2 (pseudogenes in rice and maize; Hiratsuka et al., 1989;Maier et al., 1995), rpl23 (pseudogene in spinach; Thomas et al., 1988), and infA (pseudogene in tobacco, Arabidopsis, and Oenothera elata ; Shinozaki et al., 1986;Wolfe et al., 1992b;Sato et al., 1999; Hupfer et al., 2000). Other chloroplast gene losses in angiosperms that have been confirmed by sequencing include rpl22 , rps16 , and ycf4 (open reading frame 184), all of which have been lost in 1 To whom correspondence should be addressed. E-mail (in Dublin) khwolfe@tcd.ie; fax 353-1-6798558. 646The Plant Cell some or all legumes (Gantt et al., 1991;Nagano et al., 1991; Doyle et al., 1995; K.H. Wolfe, unpublished data), and ycf2 and ndhF , both of which have been lost ...

We used DNA sequencing and gel blot surveys to assess the integrity of the chloroplast gene infA , which codes for translation initiation factor 1, in 300 diverse angiosperms. Whereas most angiosperms appear to contain an intact chloroplast infA gene, the gene has repeatedly become defunct in 24 separate lineages of angiosperms, including almost all rosid species. In four species in which chloroplast infA is defunct, transferred and expressed copies of the gene were found in the nucleus, complete with putative chloroplast transit peptide sequences. The transit peptide sequences of the nuclear infA genes from soybean and Arabidopsis were shown to be functional by their ability to target green fluorescent protein to chloroplasts in vivo. Phylogenetic analysis of infA sequences and assessment of transit peptide homology indicate that the four nuclear infA genes are probably derived from four independent gene transfers from chloroplast to nuclear DNA during angiosperm evolution. Considering this and the many separate losses of infA from chloroplast DNA, the gene has probably been transferred many more times, making infA by far the most mobile chloroplast gene known in plants.

Plants must constantly respond to changes in the environment whilst maintaining developmental and growth processes if they are to survive into the next generation. A complex network of signals from temperature and light must correctly converge to achieve successful development, through vegetative to reproductive growth. Temperature can be thought of as an environmental factor that provides both 'inductive' and 'maintenance' signals in development. It can stimulate developmental processes such as seed dormancy release, germination and vernalization. However, when temperature is not regarded as inductive, an accommodating network of genes work in concert to ensure growth responses occur regardless of fluctuating microclimate conditions. Many of the temperature-regulated developmental pathways are intimately linked with light signaling. For example, light-temperature interactions are major determinants in the timing of reproductive development. Indeed, the ability to process and react to complex environmental cues is crucial for both normal and adaptive development in a changing environment. These responses are frequently mediated by manipulating the phytohormone network, which serves as a powerful, yet adaptable controller of development. This paper illustrates the influential role temperature perception plays throughout plant development and the close interaction between temperature, light and hormone signaling.

The physiological role of class III peroxidases (EC 1.11.1.7) in controlling plant growth and development has been investigated by overexpression of both native and heterologous peroxidases. However, it has remained an enigma as to why the phenotypes of different peroxidase over-expressing transgenics vary. In order to resolve the conflicting information about the consequences of peroxidase over-expression, we have explored the role of the subcellular targeting of HRP-C in controlling stem growth, root development, axillary branching and abiotic stress tolerance in tobacco (Nicotiana tabacum L.). Altering the sub-cellular targeting of vacuolar HRP-C, such that over-expressed peroxidase accumulates in the cytoplasm and cell wall, induced phenotypic changes that are typically associated with altered auxin homeostasis, and overexpression of cell wall located peroxidases. We conclude that sub-cellular targeting is a determinant of the phenotype of peroxidase over-expressing plants.

Summary• Class III peroxidases catalyse the oxidative crosslinking of UV-absorbing phenolics. The effect of changes in the activity of phenol oxidising peroxidases (EC 1.11.1.7) on UV-tolerance in Nicotiana tabacum plants has been determined.• The UV-sensitivity of transgenic N. tabacum lines, altered in their peroxidase expression pattern, was studied by measuring radiation effects on photosynthetic efficiency.• Analysis of the effect of UV-radiation on the relative variable chlorophyll fluorescence showed that the SPI-2 line, which over-expresses a defence-related cationic peroxidase, is markedly UV-tolerant. By contrast, the ROPN3-line, which overexpresses a synthetic horseradish peroxidase-C gene, was found to be UV-sensitive. The increased activity of indole-3-acetic acid (IAA) inducible peroxidases in homozygous IAA-overproducing transgenic plants was also found to correlate with UV-sensitivity.• It is concluded that only specific peroxidase isozymes, through their effects on phenolic metabolism, contribute to the UV protection response. Thus, the analysis of the role of isozymes in UV-protection addresses fundamental questions of isozyme diversity and/or redundancy in relation to phenolic substrates.