The blue light responses and lifetime fitness of a hyper-phototropic mutant in Arabidopsis thaliana and Zea mays
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Optimal plant growth and development hinges on the plant's ability to absorb sunlight. Because plants are sessile, they have evolved a variety of responses to maximize their photosynthetic light capture. One response, called phototropism, allows plants to bend toward or away from a directional light source via blue-light (BL) induced differential cell elongation. Phototropism is mediated by a family of membrane-bound, BL-absorbing photoreceptors called the phototropins of which there are two members, phot1 and phot2. During a phototropic gain-of-function mutant screen in Arabidopsis, an allele encoding a truncated form of PHOT1, called phot1[delta]PKD, was discovered. This allele contains a premature stop codon, thus producing a protein without the C-terminal kinase signaling domain. Further analysis revealed that only plants heterozygous for PHOT1 and phot1[delta]PKD alleles display the hyper-phototropic phenotype. We hypothesize that the gain-of-function phenotype results from the heterodimerization of phot1 and phot1[delta]PKD as well as the altered subcellular localization of phot1[delta]PKD. In addition to mediating BL-induced phototropism, the phots also improve lifetime fitness. Previously work from Galen et al. (2004) has shown that field grown Arabidopsis phot1-5 and phot2-1 null mutants have reduced rates of seedling emergence from the soil, survival to flowering, and total seed set. Interestingly, Arabidopsis PHOT1/phot1[delta]PKD heterozygous plants display fitness benefits in field and greenhouse studies as measured by early bolting and increased whole plant dry weight and seed set. Though Arabidopsis is not an economically important species, such a change in a crop might be advantageous. Here, we used newly created Arabidopsis PHOT1/phot1[delta]PKD mutant lines to test BL-induced responses, analyze the subcellular localization of phot1[delta]PKD, and investigate the fitness benefits displayed in previous lines. In addition, to test fitness benefits in a crop species, maize lines containing this mutation have been generated and tested in an outdoor field setting.
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