Joseph Colasanti

The indeterminate Gene Encodes a Zinc Finger Protein and Regulates a Leaf-Generated Signal Required for the Transition to Flowering in Maize

Flowering in plants is a consequence of the transition of the shoot apex from vegetative to reproductive growth in response to environmental and internal signals. The indeterminate1 gene (id1) controls the transition to flowering in maize. We show by cloning the id1 gene that it encodes a protein with zinc finger motifs, suggesting that the id1 gene product functions as a transcriptional regulator of the floral transition. id1 mRNA expression studies and analyses of transposon-induced chimeric plants indicate that id1 acts non-cell-autonomously to regulate the production of a transmissible signal in the leaf that elicits the transformation of the shoot apex to reproductive development. These results provide molecular and genetic data consistent with the florigen hypothesis derived from classical plant physiology studies.

Rice Indeterminate 1 (OsId1) is necessary for the expression of Ehd1 (Early heading date 1) regardless of photoperiod.

Indeterminate 1 (Id1), a classical flowering gene first reported in 1946, is one of the earliest genes whose expression in leaf tissues affects the floral transition in the shoot meristem. How Id1 is integrated into the flowering process is largely unknown. In this study, we examined the genetic action of the rice (Oryza sativa) ortholog OsId1. In rice, OsId1 is preferentially expressed in young leaves, but the overall expression pattern is broader than that in maize (Zea mays). OsId1 is able to activate transcription in yeast. RNAi mutants show a delay in flowering under both short-day (SD) and long-day (LD) conditions. OsId1 regulates the expression of Ehd1 (Early heading date 1) and its downstream genes, including Hd3a (a rice ortholog of FT) and RFT1 (Rice Flowering Locus T1), under both SD and LD conditions. In rice, the expression of Ehd1 is also controlled by the photoperiodic flowering genes OsGI (a rice ortholog of GI) and OsMADS51. However, the expression of OsId1 is independent of OsGI, OsMADS51, and OsMADS50 (a rice SOC1 ortholog). This study demonstrates that the activation of Ehd1 by OsId1 is required for the promotion of flowering.

The role of epigenetic processes in controlling flowering time in plants exposed to stress

Plants interact with their environment by modifying gene expression patterns. One mechanism for this interaction involves epigenetic modifications that affect a number of aspects of plant growth and development. Thus, the epigenome is highly dynamic in response to environmental cues and developmental changes. Flowering is controlled by a set of genes that are affected by environmental conditions through an alteration in their expression pattern. This ensures the production of flowers even when plants are growing under adverse conditions, and thereby enhances transgenerational seed production. In this review recent findings on the epigenetic changes associated with flowering in Arabidopsis thaliana grown under abiotic stress conditions such as cold, drought, and high salinity are discussed. These epigenetic modifications include DNA methylation, histone modifications, and the production of micro RNAs (miRNAs) that mediate epigenetic modifications. The roles played by the phytohormones abscisic acid (ABA) and auxin in chromatin remodelling are also discussed. It is shown that there is a crucial relationship between the epigenetic modifications associated with floral initiation and development and modifications associated with stress tolerance. This relationship is demonstrated by the common epigenetic pathways through which plants control both flowering and stress tolerance, and can be used to identify new epigenomic players.

A floret by any other name: control of meristem identity in maize.

The life of a plant unfolds as a series of developmental stages, with each stage defined by changes in meristem identity. In maize, there are several distinct stages: the transition from vegetative growth to flowering, the elaboration of the inflorescence, and the formation of flowers. Progress in understanding meristem identity and function has been made by analyzing maize mutants with defects at each of these stages. Recently cloned genes suggest that, although the molecular mechanisms controlling floral organ identity are conserved in maize and other model species, the control of meristem identity during earlier developmental stages might be less conserved.

The maize INDETERMINATE1 flowering time regulator defines a highly conserved zinc finger protein family in higher plants.

BackgroundThe maize INDETERMINATE1 gene, ID1, is a key regulator of the transition to flowering and the founding member of a transcription factor gene family that encodes a protein with a distinct arrangement of zinc finger motifs. The zinc fingers and surrounding sequence make up the signature ID domain (IDD), which appears to be found in all higher plant genomes. The presence of zinc finger domains and previous biochemical studies showing that ID1 binds to DNA suggests that members of this gene family are involved in transcriptional regulation.ResultsComparison of IDD genes identified in Arabidopsis and rice genomes, and all IDD genes discovered in maize EST and genomic databases, suggest that ID1 is a unique member of this gene family. High levels of sequence similarity amongst all IDD genes from maize, rice and Arabidopsis suggest that they are derived from a common ancestor. Several unique features of ID1 suggest that it is a divergent member of the maize IDD family. Although no clear ID1 ortholog was identified in the Arabidopsis genome, highly similar genes that encode proteins with identity extending beyond the ID domain were isolated from rice and sorghum. Phylogenetic comparisons show that these putative orthologs, along with maize ID1, form a group separate from other IDD genes. In contrast to ID1 mRNA, which is detected exclusively in immature leaves, several maize IDD genes showed a broad range of expression in various tissues. Further, Western analysis with an antibody that cross-reacts with ID1 protein and potential orthologs from rice and sorghum shows that all three proteins are detected in immature leaves only.ConclusionComparative genomic analysis shows that the IDD zinc finger family is highly conserved among both monocots and dicots. The leaf-specific ID1 expression pattern distinguishes it from other maize IDD genes examined. A similar leaf-specific localization pattern was observed for the putative ID1 protein orthologs from rice and sorghum. These similarities between ID1 and closely related genes in other grasses point to possible similarities in function.

Mechanisms of Floral Induction in Grasses: Something Borrowed, Something New

Almost all that is known about the transition to flowering in grasses is based on studies of agronomic species. The grain produced by two tropically derived grasses, maize ( Zea mays ) and rice ( Oryza sativa ), and a temperate origin grass, wheat ( Triticum aestivum ), provides most of the worlds

'Florigen' enters the molecular age: long-distance signals that cause plants to flower

The transition from vegetative to reproductive growth is a critical event in the life cycle of plants. Previous physiological studies have deduced that hormone-like substances mediate this important transition but the biochemical nature of the putative signaling molecules has remained elusive. Recent molecular and genetic studies of key flowering-time genes offer new approaches to understanding the mechanisms underlying the initiation of flowering.

ZCN8 encodes a potential orthologue of Arabidopsis FT florigen that integrates both endogenous and photoperiod flowering signals in maize

Higher plants use multiple perceptive measures to coordinate flowering time with environmental and endogenous cues. Physiological studies show that florigen is a mobile factor that transmits floral inductive signals from the leaf to the shoot apex. Arabidopsis FT protein is widely regarded as the archetype florigen found in diverse plant species, particularly in plants that use inductive photoperiods to flower. Recently, a large family of FT homologues in maize, the Zea CENTRORADIALIS (ZCN) genes, was described, suggesting that maize also contains FT-related proteins that act as a florigen. The product of one member of this large family, ZCN8, has several attributes that make it a good candidate as a maize florigen. Mechanisms underlying the floral transition in maize are less well understood than those of other species, partly because flowering in temperate maize is dependent largely on endogenous signals. The maize indeterminate1 (id1) gene is an important regulator of maize autonomous flowering that acts in leaves to mediate the transmission or production of florigenic signals. This study finds that id1 acts upstream of ZCN8 to control its expression, suggesting a possible new link to flowering in day-neutral maize. Moreover, in teosinte, a tropical progenitor of maize that requires short-day photoperiods to induce flowering, ZCN8 is highly up-regulated in leaves under inductive photoperiods. Finally, vascular-specific expression of ZCN8 in Arabidopsis complements the ft-1 mutation, demonstrating that leaf-specific expression of ZCN8 can induce flowering. These results suggest that ZCN8 may encode a florigen that integrates both endogenous and environmental signals in maize.

The SEPALLATA MADS‐box protein SLMBP21 forms protein complexes with JOINTLESS and MACROCALYX as a transcription activator for development of the tomato flower abscission zone

Organ abscission is a key step in a plants life cycle and is one of the most important agronomic traits for crops. In tomato, two MADS-box genes, JOINTLESS (J) and MACROCAYLYX (MC), have been shown to be implicated in development of the flower abscission zone (AZ), but the molecular mechanisms underlying this process are not well known. We report here that the SEPALLATA (SEP) MADS-box gene SLMBP21 acts as an additional factor for development of the AZ in tomato. We show that knockdown of SLMBP21 abolishes development of the flower AZ, while overexpression of SLMBP21 produces small cells at the proximal section of the pedicel and the peduncle. Bimolecular fluorescence complementation analysis confirms that SLMBP21 interacts with J and MC, and co-immunoprecipitation assays further demonstrates that these three proteins may form higher-order protein complexes. In situ hybridization shows that SLMBP21, J, and MC transcripts accumulate in distinct regions, but overlap at the AZ vasculature. In addition, transactivation assays in yeast show that, of the three interacting proteins, only SLMBP21 can activate reporter gene transcription. RNA-seq analysis furthermore reveals that loss of function of SLMBP21, J, or MC affects a common subset of meristem activity genes including LeWUS and LATERAL SUPPRESSOR that were specifically expressed in the AZ on the tomato flower pedicel. Since SLMBP21 belongs to the FBP9/23 subclade of the SEP gene family, which is absent in Arabidopsis, the SLMBP21-J-MC complex may represent a distinct mechanism for development of the AZ in plants.

A Developmental Transcriptional Network for Maize Defines Coexpression Modules

Analyzing transcript abundance between tissues and during development identifies sets of coexpressed genes and related transcriptional controls. Here, we present a genome-wide overview of transcriptional circuits in the agriculturally significant crop species maize (Zea mays). We examined transcript abundance data at 50 developmental stages, from embryogenesis to senescence, for 34,876 gene models and classified genes into 24 robust coexpression modules. Modules were strongly associated with tissue types and related biological processes. Sixteen of the 24 modules (67%) have preferential transcript abundance within specific tissues. One-third of modules had an absence of gene expression in specific tissues. Genes within a number of modules also correlated with the developmental age of tissues. Coexpression of genes is likely due to transcriptional control. For a number of modules, key genes involved in transcriptional control have expression profiles that mimic the expression profiles of module genes, although the expression of transcriptional control genes is not unusually representative of module gene expression. Known regulatory motifs are enriched in several modules. Finally, of the 13 network modules with more than 200 genes, three contain genes that are notably clustered (P < 0.05) within the genome. This work, based on a carefully selected set of major tissues representing diverse stages of maize development, demonstrates the remarkable power of transcript-level coexpression networks to identify underlying biological processes and their molecular components.