B-function expression in the flower center underlies the homeotic phenotype of Lacandonia schismatica (Triuridaceae).
Spontaneous homeotic transformations have been described in natural populations of both plants and animals, but little is known about the molecular-genetic mechanisms underlying these processes in plants. In the ABC model of floral organ identity in Arabidopsis thaliana, the B- and C-functions are necessary for stamen morphogenesis, and C alone is required for carpel identity. We provide ABC model-based molecular-genetic evidence that explains the unique inside-out homeotic floral organ arrangement of the monocotyledonous mycoheterotroph species Lacandonia schismatica (Triuridaceae) from Mexico. Whereas a quarter million flowering plant species bear central carpels surrounded by stamens, L. schismatica stamens occur in the center of the flower and are surrounded by carpels. The simplest explanation for this is that the B-function is displaced toward the flower center. Our analyses of the spatio-temporal pattern of B- and C-function gene expression are consistent with this hypothesis. The hypothesis is further supported by conservation between the B-function genes of L. schismatica and Arabidopsis, as the former are able to rescue stamens in Arabidopsis transgenic complementation lines, and Ls-AP3 and Ls-PI are able to interact with each other and with the corresponding Arabidopsis B-function proteins in yeast. Thus, relatively simple molecular modifications may underlie important morphological shifts in natural populations of extant plant taxa.
Laboratorio de Genética Molecular, Desarrollo y Evolución de Plantas, Departamento de Ecología Funcional, Instituto de Ecología, Universidad Nacional Autónoma de México, Tercer Circuito Exterior, Ciudad Universitaria, D.F. Mexico 04510, Mexico. eabuylla@gmail.com
Elena R
ER
Álvarez-Buylla
Barbara A
BA
Ambrose
Eduardo
E
Flores-Sandoval
Marie
M
Englund
Adriana
A
Garay-Arroyo
Berenice
B
García-Ponce
Eduardo
E
de la Torre-Bárcena
Silvia
S
Espinosa-Matías
Esteban
E
Martínez
Alma
A
Piñeyro-Nelson
Peter
P
Engström
Elliot M
EM
Meyerowitz
D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000033:anatomy & histology / Q000235:genetics / Q000254:growth & development; D035264:Flowers / Q000033:anatomy & histology* / Q000235:genetics* / Q000254:growth & development; D018506:Gene Expression Regulation, Plant; D005801:Genes, Homeobox; D017343:Genes, Plant; D005816:Genetic Complementation Test; D026161:MADS Domain Proteins / Q000235:genetics; D019684:Magnoliopsida / Q000033:anatomy & histology* / Q000235:genetics* / Q000254:growth & development; D008969:Molecular Sequence Data; D009024:Morphogenesis / Q000235:genetics; D010641:Phenotype; D010802:Phylogeny; D010940:Plant Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics; D016415:Sequence Alignment; D020798:Two-Hybrid System Techniques
D026161:MADS Domain Proteins; D010940:Plant Proteins