ZmPIN1aandZmPIN1bEncode Two Novel Putative Candidates for Polar Auxin Transport and Plant Architecture Determination of Maize

Abstract

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.

Transcriptomic Analyses Indicate That Maize Ligule Development Recapitulates Gene Expression Patterns That Occur during Lateral Organ Initiation

“…Hormonal signaling networks typically associated with organogenesis and branching are also recapitulated during ligule biogenesis in the young primordium. PIN1 accumulation within the PLB strongly resembles PIN1 maxima at the site of leaf initiation (Figures 7A to 7D) (Carraro et al, 2006;Gallavotti et al, 2008;Lee et al, 2009). Our data support a model in which KNOX accumulation at the base of the leaf primordium and auxin accumulation and signaling in the distal portion of the primordium provide positional cues that demarcate the blade-sheath boundary.…”

“…These include four PIN-like genes, previously described to function during the earliest known events in lateral organ initiation (Benková et al, 2003;Reinhardt et al, 2003;Carraro et al, 2006;Gallavotti et al, 2008;Lee et al, 2009), that are upregulated in the preligule L1 ( Figures 4D and 4E). These data are consistent with previous reports that ZmPIN1a-YFP accumulates in the PLB (Moon et al, 2013) (Figures 1I and 1J).…”

Hormonal Regulation of Branching in Grasses

“…Three PIN1 loci have been identified in maize and rice (Xu et al, 2005;Carraro et al, 2006;Gallavotti et al, 2008b). The maize ZmPIN1a gene complements the Arabidopsis pin1 mutant, restoring its ability to make flowers, indicating that ZmPIN1a likely functions in auxin transport in maize (Gallavotti et al, 2008b).…”

Combined Large-Scale Phenotyping and Transcriptomics in Maize Reveals a Robust Growth Regulatory Network

“…The latter shows homology to Arabidopsis GTL1, a master regulator that negatively regulates cell growth (Breuer et al, 2012). Other examples of genes in this subnetwork that were already functionally annotated were ZmPIN1b, an auxin efflux carrier (Carraro et al, 2006), and Zmb-GLUCOSIDASE1, involved in the (in)activation of cytokinins (Brzobohatý et al, 1993). Subnetwork 3 consisted of 45 genes that were primarily positively correlated to leaf size and timing traits (Fig.…”