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MADS about the evolution of orchid flowers

2008; Elsevier BV; Volume: 13; Issue: 2 Linguagem: Inglês

10.1016/j.tplants.2007.11.007

1878-4372

Mariana Mondragón‐Palomino, Günter Theißen,

Plant and animal studies

Orchids have unique flowers involving three types of perianth organs: outer tepals, lateral inner tepals, and a lip. Expression studies indicate that the identity of these organs is specified by the combinatorial interaction of four different DEFICIENS-like MADS-box genes. We suggest that clarifying the evolution of these genes provides a rational framework for reconstructing the enigmatic origin and unique diversification of the orchid flower. For example, two rounds of gene duplications during early orchid evolution might have generated the genes that were probably recruited to distinguish the different types of perianth organs. This hypothesis suggests intriguing, experimentally testable mechanisms by which gene duplications followed by sub- and neo-functionalization events might have contributed to the evolutionary origin of morphological novelties in orchids – and well beyond. Orchids have unique flowers involving three types of perianth organs: outer tepals, lateral inner tepals, and a lip. Expression studies indicate that the identity of these organs is specified by the combinatorial interaction of four different DEFICIENS-like MADS-box genes. We suggest that clarifying the evolution of these genes provides a rational framework for reconstructing the enigmatic origin and unique diversification of the orchid flower. For example, two rounds of gene duplications during early orchid evolution might have generated the genes that were probably recruited to distinguish the different types of perianth organs. This hypothesis suggests intriguing, experimentally testable mechanisms by which gene duplications followed by sub- and neo-functionalization events might have contributed to the evolutionary origin of morphological novelties in orchids – and well beyond. (Flower) with two or more planes of symmetry. Also referred to as polysymmetric or radially symmetric. Group of taxonomic units (species, genes) consisting of a single hypothetical ancestor and all of its descendants; also referred to as monophyletic group. An evolutionary innovation that opens up possibilities for the exploitation of new ecological niches and triggers the adaptive radiation of the group of organisms that have such a trait. Refers to the four founding genes of the MADS-box gene family, that is, MCM1 (MINICHROMOSOME MAINTENANCE 1), AG (AGAMOUS), DEF (DEFICIENS), SRF (SERUM RESPONSE FACTOR). Domain structure of a protein, comprising a MADS domain followed by an Intervening domain, a Keratin-like domain and a C-terminal domain. Refers to the organization of multicellular organisms into developmentally and anatomically distinct parts, or to the organization of gene regulatory regions into discrete ‘cis-regulatory elements’. When one of two duplicate genes acquires a mutation that enables the gene to take on a new function. When one of two duplicate genes acquires a mutation that renders the gene non-functional. A gene that originated by a gene duplication event. The sterile floral organs ‘around the anthers’ (i.e. the sepals, petals, or tepals). A process during which, after gene duplication, the function of an original gene is divided between the paralogous descendants of the original gene (‘job sharing’ at gene level). Sub-functionalization often works through degenerative mutations in different cis-regulatory elements of genes, thus leading to restricted but complementary expression domains of the duplicate genes. refers to the founding members of the gene family – TB1 (TEOSINTE BRANCHED 1) from maize, CYC (CYCLOIDEA) from Antirrhinum, PCF1 and PCF2 (PROLIFERATING CELL NUCLEAR ANTIGEN GENE-CONTROLLING ELEMENT BINDING FACTOR 1 and 2). (Flower) with a single plane of symmetry in which one half mirrors the other half. Also referred to as monosymmetric and bilaterally symmetric.