The highs and lows of plant life: temperature and light interactions in development.

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.

Transgenic tobacco (Nicotiana tabacum L. cv. Samsun-NN) plants over-expressing a synthetic HRP-C gene are altered in growth, development and susceptibility to abiotic stress.

The physiological role of class III peroxidases (EC 1.11.1.7) in controlling plant growth and development has been investigated by over-expression 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 over-expression of cell wall located peroxidases. We conclude that sub-cellular targeting is a determinant of the phenotype of peroxidase over-expressing plants.

An N-terminal peptide extension results in efficient expression, but not secretion, of a synthetic horseradish peroxidase gene in transgenic tobacco.

BACKGROUND AND AIMS: Native horseradish (Armoracia rusticana) peroxidase, HRP (EC 1.11.1.7), isoenzyme C is synthesized with N-terminal and C-terminal peptide extensions, believed to be associated with protein targeting. This study aimed to explore the specific functions of these extensions, and to generate transgenic plants with expression patterns suitable for exploring the role of peroxidase in plant development and defence. METHODS: Transgenic Nicotiana tabacum (tobacco) plants expressing different versions of a synthetic horseradish peroxidase, HRP, isoenzyme C gene were constructed. The gene was engineered to include additional sequences coding for either the natural N-terminal or the C-terminal extension or both. These constructs were placed under the control of a constitutive promoter (CaMV-35S) or the tobacco RUBISCO-SSU light inducible promoter (SSU) and introduced into tobacco using Agrobacterium-mediated transformation. To study the effects of the N- and C-terminal extensions, the localization of recombinant peroxidase was determined using biochemical and molecular techniques. KEY RESULTS: Transgenic tobacco plants can exhibit a ten-fold increase in peroxidase activity compared with wild-type tobacco levels, and the majority of this activity is located in the symplast. The N-terminal extension is essential for the production of high levels of recombinant protein, while the C-terminal extension has little effect. Differences in levels of enzyme activity and recombinant protein are reflected in transcript levels. CONCLUSIONS: There is no evidence to support either preferential secretion or vacuolar targeting of recombinant peroxidase in this heterologous expression system. This leads us to question the postulated targeting roles of these peptide extensions. The N-terminal extension is essential for high level expression and appears to influence transcript stability or translational efficiency. Plants have been generated with greatly elevated cytosolic peroxidase activity, and smaller increases in apoplastic activity. These will be valuable for exploring the role of these enzymes in stress amelioration and plant development.

Over-expression of phenol-oxidising peroxidases alters the UV-susceptibility of transgenic Nicotiana tabacum.

• 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.