Received March 6, 2006
Accepted July 3, 2006
ZmPIN1a and ZmPIN1b encode two novel putative candidates for polar auxin transport and plant architecture determination of maize
Nicola Carraro , Cristian Forestan , Sabrina Canova , Jan Traas , and Serena Varotto *
Dipartimento di Agronomia Ambientale e Produzioni Vegetali, Università degli Studi di Padova Agripolis - Viale dell'Università 16, 35020 Legnaro, Padova, Italy
Laboratoire de Reproduction et Développement des Plantes, ENS-Lyon, 46 allée d'Italie, 69364 Lyon, France.
* Corresponding author; email: serena.varotto{at}unipd.it.
Shoot Apical Meristems (SAMs) produce organs in a highly stereotypic pattern that involves auxin. Auxin is supposed to be actively transported from cell to cell by influx (AUX/LAX proteins) and efflux membrane carriers (PIN proteins). Current hypotheses propose that at the meristem surface PIN proteins create patterns of auxin gradients that, in turn, create patterns of gene expression and morphogenesis. These hypotheses are entirely based on work in Arabidopsis thaliana. To verify if these models also apply for other species, we studied the behaviour of PIN proteins during Zea mays development. We identified two novel putative orthologs of AtPIN1 in maize and analyzed their expression pattern during development. The expression studies were complemented by immunolocalization studies using an anti-AtPIN1 antibody. Interestingly, the maize proteins visualized by this antibody are almost exclusively localized in sub-epidermal meristematic layers. Both tassel and ear were characterized by a compact group of cells just below the surface, carrying PIN. In contrast to, or in complement of what was shown in Arabidopsis, these results point at the importance of internally localized cells in the patterning process. We chose the barren inflorescence2 maize mutant to study the role of auxin polar fluxes in inflorescence development. In severe alleles of bif2 the tassel and the ear present altered ZmPIN1a and ZmPIN1b protein expression and localization patterns. In particular the compact groups of cells in the tassel and ear of the mutant were missing. We conclude that BIF2 is important for PIN organisation and could play a role in the establishment of polar auxin fluxes in the maize inflorescence, indirectly modulating the process of axillary meristem formation and development.
