The FT-Like ZCN8 Gene Functions as a Floral Activator and Is Involved in Photoperiod Sensitivity in Maize[C][W][OA]

The transition from vegetative to reproductive development is regulated by the activity of graft-transmissible flowering hormone, florigen, which is encoded by the FLOWERING LOCUS T (FT) family of mobile proteins. This work identified, among many maize FT-like genes, a single gene, ZCN8, which has all required characteristics to function as florigen

Concerted Modification of Flowering Time and Inflorescence Architecture by Ectopic Expression of TFL1-Like Genes in Maize1[W][OA]

TERMINAL FLOWER1 (TFL1)-like genes are highly conserved in plants and are thought to function in the maintenance of meristem indeterminacy. Recently, we described six maize (Zea mays) TFL1-related genes, named ZEA CENTRORADIALIS1 (ZCN1) to ZCN6. To gain insight into their functions, we generated transgenic maize plants overexpressing their respective cDNAs driven by a constitutive promoter. Overall, ectopic expression of the maize TFL1-like genes produced similar phenotypes, including delayed flowering and altered inflorescence architecture. We observed an apparent relationship between the magnitude of the transgenic phenotypes and the degree of homology between the ZCN proteins. ZCN2, -4, and -5 form a monophylogenetic clade, and their overexpression produced the strongest phenotypes. Along with very late flowering, these transgenic plants produced a “bushy” tassel with increased lateral branching and spikelet density compared with nontransgenic siblings. On the other hand, ZCN1, -3, and -6 produced milder effects. Among them, ZCN1 showed moderate effects on flowering time and tassel morphology, whereas ZCN3 and ZCN6 did not change flowering time but still showed effects on tassel morphology. In situ hybridizations of tissue from nontransgenic plants revealed that the expression of all ZCN genes was associated with vascular bundles, but each gene had a specific spatial and temporal pattern. Expression of four ZCN genes localized to the protoxylem, whereas ZCN5 was expressed in the protophloem. Collectively, our findings suggest that ectopic expression of the TFL1-like genes in maize modifies flowering time and inflorescence architecture through maintenance of the indeterminacy of the vegetative and inflorescence meristems

Beyond flowering time: Pleiotropic function of the maize flowering hormone florigen

The transition from vegetative to reproductive development is a critical turning point in a plant's life cycle. It is now widely accepted that a leaf-borne signal, florigen, moves via the phloem from leaves to the shoot apical meristem to trigger its reprogramming to produce flowers.1 In part, the florigenic signal comprises a protein that belongs to the phosphatidylethanolamine-binding protein (PEBP) family that is present in all living organisms but displays diverse functions. The founding floral-promoting PEBP gene in Arabidopsis is FLOWERING LOOCUS T (FT) whose functional homologs have been indentified in many flowering plants. We recently accumulated sufficient evidence to demonstrate the maize FT homolog ZCN8 has florigenic function. This task was particularly challenging due to the large number of FT-homologous genes in the maize genome. Here we show that ZCN8 function is more complex than simply regulating the floral transition. ZCN8 appears to play a pleiotropic role in the regulation of generalized growth of vegetative and reproductive tissues

Disruption of Imprinting by Mutator Transposon Insertions in the 5′ Proximal Regions of the Zea mays Mez1 Locus

Imprinting is a form of epigenetic gene regulation in which alleles are differentially regulated according to the parent of origin. The Mez1 gene in maize is imprinted such that the maternal allele is expressed in the endosperm while the paternal allele is not expressed. Three novel Mez1 alleles containing Mutator transposon insertions within the promoter were identified. These mez1-mu alleles do not affect vegetative expression levels or result in morphological phenotypes. However, these alleles can disrupt imprinted expression of Mez1. Maternal inheritance of the mez-m1 or mez1-m4 alleles results in activation of the normally silenced paternal allele of Mez1. Paternal inheritance of the mez1-m2 or mez1-m4 alleles can also result in a loss of silencing of the paternal Mez1 allele. The paternal disruption of imprinting by transposon insertions may reflect a requirement for sequence elements involved in targeting silencing of the paternal allele. The maternal disruption of imprinting by transposon insertions within the Mez1 promoter suggests that maternally produced MEZ1 protein may be involved in silencing of the paternal Mez1 allele. The endosperms with impaired imprinting did not exhibit phenotypic consequences associated with bi-allelic Mez1 expression

A Genomic and Expression Compendium of the Expanded PEBP Gene Family from Maize[W][OA]

The phosphatidylethanolamine-binding proteins (PEBPs) represent an ancient protein family found across the biosphere. In animals they are known to act as kinase and serine protease inhibitors controlling cell growth and differentiation. In plants the most extensively studied PEBP genes, the Arabidopsis (Arabidopsis thaliana) FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1) genes, function, respectively, as a promoter and a repressor of the floral transition. Twenty-five maize (Zea mays) genes that encode PEBP-like proteins, likely the entire gene family, were identified and named Zea mays CENTRORADIALIS (ZCN), after the first described plant PEBP gene from Antirrhinum. The maize family is expanded relative to eudicots (typically six to eight genes) and rice (Oryza sativa; 19 genes). Genomic structures, map locations, and syntenous relationships with rice were determined for 24 of the maize ZCN genes. Phylogenetic analysis assigned the maize ZCN proteins to three major subfamilies: TFL1-like (six members), MOTHER OF FT AND TFL1-like (three), and FT-like (15). Expression analysis demonstrated transcription for at least 21 ZCN genes, many with developmentally specific patterns and some having alternatively spliced transcripts. Expression patterns and protein structural analysis identified maize candidates likely having conserved gene function of TFL1. Expression patterns and interaction of the ZCN8 protein with the floral activator DLF1 in the yeast (Saccharomyces cerevisiae) two-hybrid assay strongly supports that ZCN8 plays an orthologous FT function in maize. The expression of other ZCN genes in roots, kernels, and flowers implies their involvement in diverse developmental processes

Duplicated fie Genes in Maize: Expression Pattern and Imprinting Suggest Distinct Functions

Two maize genes with predicted translational similarity to the Arabidopsis FIE (Fertilization-Independent Endosperm) protein, a repressor of endosperm development in the absence of fertilization, were cloned and analyzed. Genomic sequences of fie1 and fie2 show significant homology within coding regions but none within introns or 5′ upstream. The fie1 gene is expressed exclusively in the endosperm of developing kernels starting at ∼6 days after pollination. fie1 is an imprinted gene showing no detectable expression of the paternally derived fie1 allele during kernel development. Conversely, fie2 is expressed in the embryo sac before pollination. After pollination, its expression persists, predominantly in the embryo and at lower levels in the endosperm. The paternal fie2 allele is not expressed early in kernel development, but its transcription is activated at 5 days after pollination. fie2 is likely to be a functional ortholog of the Arabidopsis FIE gene, whereas fie1 has evolved a distinct function. The maize FIE2 and sorghum FIE proteins form a monophyletic group, sharing a closer relationship to each other than to the FIE1 protein, suggesting that maize fie genes originated from two different ancestral genomes

Over-expression of the photoperiod response regulator ZmCCT10 modifies plant architecture, flowering time and inflorescence morphology in maize.

Maize originated as a tropical plant that required short days to transition from vegetative to reproductive development. ZmCCT10 [CO, CONSTANS, CO-LIKE and TIMING OF CAB1 (CCT) transcription factor family] is a regulator of photoperiod response and was identified as a major QTL controlling photoperiod sensitivity in maize. We modulated expression of ZmCCT10 in transgenic maize using two constitutive promoters with different expression levels. Transgenic plants over expressing ZmCCT10 with either promoter were delayed in their transition from vegetative to reproductive development but were not affected in their switch from juvenile-to-adult vegetative growth. Strikingly, transgenic plants containing the stronger expressing construct had a prolonged period of vegetative growth accompanied with dramatic modifications to plant architecture that impacted both vegetative and reproductive traits. These plants did not produce ears, but tassels were heavily branched. In more than half of the transgenic plants, tassels were converted into a branched leafy structure resembling phyllody, often composed of vegetative plantlets. Analysis of expression modules controlling the floral transition and meristem identity linked these networks to photoperiod dependent regulation, whereas phase change modules appeared to be photoperiod independent. Results from this study clarified the influence of the photoperiod pathway on vegetative and reproductive development and allowed for the fine-tuning of the maize flowering time model