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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

ZmPIN1a and ZmPIN1b Encode Two Novel Putative Candidates for Polar Auxin Transport and Plant Architecture Determination of Maize^1,[W]

Dipartimento di Agronomia Ambientale e Produzioni Vegetali, Università degli Studi di Padova Agripolis–Viale dell'Università 16, 35020 Legnaro (PD), Italy (N.C., C.F., S.C., S.V.); and Laboratoire de Reproduction et Développement des Plantes, École Normale Supérieure-Lyon, 69364 Lyon, France (J.T.)

Shoot apical meristems produce organs in a highly stereotypic pattern that involves auxin. Auxin is supposed to be actively transported from cell to cell by influx (AUXIN/LIKE AUXIN proteins) and efflux (PIN-FORMED proteins) membrane carriers. 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 (Arabidopsis thaliana). To verify whether these models also apply to other species, we studied the behavior of PIN proteins during maize (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 subepidermal meristematic layers. Both tassel and ear were characterized by a compact group of cells, just below the surface, carrying PIN. In contrast to or to complement what was shown in Arabidopsis, these results point to the importance of internally localized cells in the patterning process. We chose the barren inflorescence2 (bif2) 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 organization and could play a role in the establishment of polar auxin fluxes in maize inflorescence, indirectly modulating the process of axillary meristem formation and development.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Serena Varotto (serena.varotto{at}unipd.it).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.080119

^* Corresponding author; e-mail serena.varotto{at}unipd.it; fax 39–049–8272839.

Received March 6, 2006; accepted July 3, 2006.