Photoreceptor cross-talk in UV-B photomorphogenesis in tomato (Solanum lycopersicum) : screening through phytochrome and cryptochrome mutants : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology at Massey University, Palmerston North, New Zealand
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Date
2017
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Massey University
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Abstract
Plant photoreceptors detect changes in the light environment and induce differential gene
expression, resulting in the appropriate physiological and morphological responses. Under full
sunlight, phytochromes, cryptochromes and the UV-B photoreceptor, UVR8 (UV-B
RESISTANCE LOCUS 8), destabilize PHYTOCHROME INTERACTING FACTORS (PIFs)
to inhibit elongation. PIFs are transcriptions factors that inhibit light-regulated genes, including
auxin-related genes involved in cell elongation. In the shaded environment, the reduction in
the spectral composition detected by the photoreceptors results in the activation of elongation
and PIF activity. However, recent studies have shown that low levels of UV-B can still inhibit
the elongation under shade.
Most photobiology studies that investigated plant responses to shade have concentrated on the
model species, Arabidopsis thaliana. In contrast, Solanum lycopersicum (tomato) is another
model system, but few studies have investigated plant responses to shade in tomato due to its
sympodial architecture and presence of internodes which A. thaliana lacks. In this study,
phytochrome and cryptochrome tomato mutants were exposed to low levels of UV-B under
photosynthetically active radiation (PAR) as background light to investigate the possible crosstalk
between these photoreceptors and the UV-B photoreceptor of tomato in regulating
hypocotyl or internode elongation. Out of all the multiple phytochrome and one cryptochrome
mutants, phyAphyB2 mutant exhibited an impaired UV-B inhibition of internode elongation
after three days of UV-B treatment. End-point PCR on the gene expression of PIF4 together
with two UV-B responsive genes and genes involved in the catabolism of active gibberellin
could not explain the impaired response of phyAphyB2. Nevertheless, physiological
measurements indicate that phyA and phyB2 of tomato may be acting redundantly in mediating
the UV-B induced inhibition of internode.
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Figures 1.1, 1.3, 1.4 and 1.5 removed for copyright reasons
Keywords
Tomatoes, Photomorphogenesis, Photoreceptors, Research Subject Categories::NATURAL SCIENCES::Biology::Organism biology::Plant physiology