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Molecular ecology of plant-pollinator interactions |
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| P. integrifolia ssp. inflata is pollinated by solitary bees |
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P. axillaris ssp parodii is pollinated by nocturnal hawkmoths |
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P. exserta is pollinated by hummingbirds. The plant is extremely rare in nature. In 2006, only 14 plants were found. A major threat is hybridization with P. axillaris |
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P. axillaris and P. integrifolia can be found growing side by side in their natural habitat. Here a picture from Nuevo Berlin, Uruguay, November 2002. Even though they can easily be crossed in the laboratory, no hybrids have been found in nature. This is caused at least in part by the fact that they attract different pollinators.
The three wild Petunia species are closely related and can easily be crossed in the laboratory. Our aim is to identify the genes that specify the divergent pollination syndromes. Importantly, many of the different Petunia species can be crossed with each other and with the transposon line W138.
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We make use of the P. hybrida line W138. Its extremely active endogenous dTph1 transposon system allows for efficient forward and reverse genetics. All commercial Petunias are thought to be hybrids between P. axillaris and P. integrifolia. Petunia hybrida are hardy and undemanding plants with a life cycle of only 8-12 weeks. The plants can proliferate into large bushes, but can also be manipulated to flower early. Even when planted at a density of 75-100 per m2 they can produce thousands of seeds per plant. The genome is slightly larger than tomato (1.2 Mkb) and approximately 8 times the size of Arabidopsis. Petunia is closely related to tomato, potato and tobacco, so that most basic processes are conserved and genomic data can easily be transferred between these species.
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We crossed each of the wild species P. axillaris and P. integrifolia with the transposon line P. hybrida W138 and constructed recombinant inbred lines (RILs). QTL mapping detected major QTLs for all the traits of the bee- and hawkmoth pollination syndromes: color, scent, floral architecture and nectar quality and quantity. The excellent forward and reverse genetics available in Petunia offer great opportunities for the identification of the genes behind these QTLs
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Recombinant inbred lines between P. integrifolia ssp. inflata and P. hybrida W138 |
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An important gene is An2. It encodes a transcription factor that regulates the synthesis of anthocyanin, the purple pigment that is present in P. integrifolia but absent in P. axillaris. An2 is active in P. integrifolia, but in all P. axillaris accessions tested An2 is rendered inactive by mutations in the coding region. When an active An2 gene derived P. integrifolia was introduced into P. axillaris via Agrobacterium-mediated transformation, the transgenic plants had purple flowers but were otherwise indistinguishable from P. axillaris.
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Left: P. axillaris; right, P. axillaris transformed with the P. integrifolia An2 gene.
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In choice experiments, bees visited the transgenics more frequently, while hawkmoths strongly favored the white-colored wild plants.
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For the future, we are planning to pursue further candidate gene approaches, especially for genes involving fragrance production. A combination with breeding and genomics approaches will be used to understand the genetic basis of the differences in flower morphology. |
Development of molecular markers for genetic mapping in Petunia [pdf - 870 KB]
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