Molecular Analysis of the SCARECROW Gene in Maize Reveals a Common Basis for Radial Patterning in Diverse Meristems (original) (raw)

Diversity of Maize Shoot Apical Meristem Architecture and Its Relationship to Plant Morphology

G3 (Bethesda, Md.), 2015

The shoot apical meristem contains a pool of undifferentiated stem cells and controls initiation of all aerial plant organs. In maize (Zea mays), leaves are formed throughout vegetative development; upon transition to floral development, the shoot meristem forms the tassel. Due to the regulated balance between stem cell maintenance and organogenesis, the structure and morphology of the shoot meristem is constrained during vegetative development. Previous work identified loci controlling meristem architecture in a recombinant inbred line population. The study presented here expanded upon this by investigating shoot apical meristem morphology across a diverse set of maize inbred lines. Crosses of these lines to common parents showed varying phenotypic expression in the F1, with some form of heterosis occasionally observed. An investigation of meristematic growth throughout vegetative development in diverse lines linked the timing of reproductive transition to flowering time. Phenotypi...

The SHORT-ROOT gene controls radial patterning of the Arabidopsis root through radial signaling

2000

Asymmetric cell divisions play an important role in the establishment and propagation of the cellular pattern of plant tissues. The SHORT-ROOT (SHR) gene is required for the asymmetric cell division responsible for formation of ground tissue (endodermis and cortex) as well as specification of endodermis in the Arabidopsis root. We show that SHR encodes a putative transcription factor with homology to SCARECROW (SCR).

Three maize root-specific genes are not correctly expressed in regenerated caps in the absence of the quiescent center

Planta, 2000

The quiescent center is viewed as an architectural template in the root apical meristem of all angiosperm and gymnosperm root tips. In roots of Arabidopsis thaliana (L.) Heynh., the quiescent center inhibits differentiation of contacting initial cells and maintains the surrounding initial cells as stem cells. Here, the role of the quiescent center in the development of the maize (Zea mays L.) root cap has been further explored. Three maize root-specific genes were identified. Two of these were exclusively expressed in the root cap and one of them encoded a GDP-mannose-4,6-dehydratase. Most likely these two genes are structural, tissue-specific markers of the cap. The third gene, a putative glycine-rich cell wall protein, was expressed in the cap and in the root epidermis and, conceivably is a positional marker of the cap. Microsurgical and molecular data indicate that the quiescent center and cap initials may regulate the positional and structural expression of these genes in the cap and thereby control root cap development.

Genetic control of maize shoot apical meristem architecture

G3 (Bethesda, Md.), 2014

The shoot apical meristem contains a pool of undifferentiated stem cells and generates all above-ground organs of the plant. During vegetative growth, cells differentiate from the meristem to initiate leaves while the pool of meristematic cells is preserved; this balance is determined in part by genetic regulatory mechanisms. To assess vegetative meristem growth and genetic control in Zea mays, we investigated its morphology at multiple time points and identified three stages of growth. We measured meristem height, width, plastochron internode length, and associated traits from 86 individuals of the intermated B73 × Mo17 recombinant inbred line population. For meristem height-related traits, the parents exhibited markedly different phenotypes, with B73 being very tall, Mo17 short, and the population distributed between. In the outer cell layer, differences appeared to be related to number of cells rather than cell size. In contrast, B73 and Mo17 were similar in meristem width traits...

The SCARECROW Gene Regulates an Asymmetric Cell Division That Is Essential for Generating the Radial Organization of the Arabidopsis Root

Cell, 1996

stem cells or initials: the columella root cap initials; the *Department of Biology pericycle/vascular initials; the epidermal/lateral root cap New York University initials; and the cortex/endodermal initials (Dolan et al., New York, New York 10003 1993) (Figure 1A). It has been shown that at least some † The University of Georgia of these initials undergo asymmetric divisions (Dolan et Complex Carbohydrate Research Center al., 1993). The cortex/endodermal initial, for example, Athens, Georgia 30602-4712 first divides anticlinally (in a transverse orientation) (Fig-‡ Department of Plant Sciences ure 1B). This asymmetric division produces another ini-University of Arizona tial and a daughter cell. The daughter cell then divides Tucson, Arizona 85721 periclinally (in a longitudinal orientation) (Figure 1B). This second asymmetric division produces the progenitors of the endodermis and the cortex cell lineages (Fig-Summary ure 1B). We have identified and characterized mutations that In the Arabidopsis root meristem, initial cells undergo disrupt the asymmetric divisions of the cortex/endoderasymmetric divisions to generate the cell lineages of mal initial (Benfey et al., 1993; Scheres et al., 1995). The the root. The scarecrow mutation results in roots that short-root (shr) and scarecrow (scr) mutations result in are missing one cell layer owing to the disruption of the loss of a cell layer between the epidermis and pericyan asymmetric division that normally generates cortex cle. In both mutants, the cortex/endodermal initial diand endodermis. Tissue-specific markers indicate that vides anticlinally, but the subsequent periclinal division a heterogeneous cell type is formed in the mutant. The that increases the number of cell layers does not take deduced amino acid sequence of SCARECROW (SCR) place (Benfey et al., 1993; Scheres et al., 1995). The suggests that it is a member of a novel family of putadefect is first apparent in the embryo and extends the tive transcription factors. SCR is expressed in the corlength of the embryonic axis, which includes the embrytex/endodermal initial cells and in the endodermal cell onic root and hypocotyl (Scheres et al., 1995). This is lineage. Tissue-specific expression is regulated at the also true for the other radial organization mutants chartranscriptional level. These results indicate a key role acterized to date, suggesting that radial organization for SCR in regulating the radial organization of the that occurs during embryonic development may influroot. ence the postembryonic organization generated by the meristematic initials (Scheres et al., 1995).

Roots Redefined: Anatomical and Genetic Analysis of Root Development

Plant Physiology

The postembryonic development of plants is fueled by apical meristems, which are the local production sites of new cells that form a pattern of different cell types within an organ. The regularity of this pattern in the root yielded ideas on its formation from the meristem well before critical studies on the shoot apex were performed (e.g. Hanstein, 1870). The model plant Arabidopsis thaliana, which allows genetic dissection of root development, is a paragon of this regularity. In this Llpdate, we review recent studies on root anatomy and genetics that are allowing us to refine, and perhaps redefine, our understanding of organ development. We will focus on two pivotal aspects of root development: pattern formation and cell proliferation. Important work on other aspects of Arabidopsis roots, such as cell elongation/ morphogenesis, tropism, and cell size and shape, has been covered in recent reviews (Benfey and Schiefelbein, 1994; Dolan and Roberts, 1995) and will not be discussed here.

Tornado1 and tornado2 are required for the specification of radial and circumferential pattern in the Arabidopsis root

Development (Cambridge, England), 2000

The cell layers of the Arabidopsis primary root are arranged in a simple radial pattern. The outermost layer is the lateral root cap and lies outside the epidermis that surrounds the ground tissue. The files of epidermal and lateral root cap cells converge on a ring of initials (lateral root cap/epidermis initial) from which the epidermal and lateral root cap tissues of the seedling are derived, once root growth is initiated after germination. Each initial gives rise to a clone of epidermal cells and a clone of lateral root cap cells. These initial divisions in the epidermal/lateral root cap initial are defective in tornado1 (trn1) and trn2 plants indicating a requirement for TRN1 and TRN2 for initial cell function. Furthermore, lateral root cap cells develop in the epidermal position in trn1 and trn2 roots indicating that TRN1 and TRN2 are required for the maintenance of the radial pattern of cell specification in the root. The death of these ectopic lateral root cap cells in the e...

Formation and cell lineage patterns of the shoot apex of maize

Plant Journal, 1992

In maize, glossy (go mutants lack the wax layer normally present on the epidermis of young leaves. By insertion mutagenesis, unstable alleles (gIl-m) have been induced at the GIl locus. In the gIi-m8 strain, somatic reversions to wild-type frequently result in the formation of large sectors occupying predictable positions in all seedlings' leaves. In studies of 230 g/i-m8 seedlings with large reverted sectors covering around 50% of the first leaf, four patterns of sectoring were recognized: one large sector ending in all leaves at the main midrib (32.6% of cases); one central sector on leaves 1,3 and 5 (or 2 and 4), corresponding t o lateral stripes of GIl tissue on the other leaves (7.9%); a sector decreasing or increasing in successive leaves (9.1 YO); other types with one sector covering a leaf surface between 33 and 50% (i9.i %) or with complex variegations (31 -3%). Based on leaf sectoring, the pattern and stability of cell lineages during shoot apex establishment and embryonic activity leading t o leaf primordia, are inferred from the genetic state (GI or g/?-m) of leaf founder cells present in the apex at the ring of primordia insertion. A genetic experiment indicates that the large somatic reversions considered derived from both the LI and the LII layers of the apex. A large majority of the observed patterns of reversion can be interpreted as due to a single event of transposition. The data are discussed and relevant conclusions proposed in relation to the age of the proembryo at the time of apex formation, the permanent or impermanent state of initial cells of the apex, the polarization of cell divisions and the plane of early apex cell division as a mechanism leading to the bilateral symmetry of the maize seedling.

Lateral root development in the maize (Zea mays) lateral rootless1 mutant

Annals of Botany, 2013

† Background and Aims The maize lrt1 (lateral rootless1) mutant is impaired in its development of lateral roots during early post-embryonic development. The aim of this study was to characterize, in detail, the influences that the mutation exerts on lateral root initiation and the subsequent developments, as well as to describe the behaviour of the entire plant under variable environmental conditions. † Methods Mutant lrt1 plants were cultivated under different conditions of hydroponics, and in between sheets of moist paper. Cleared whole mounts and anatomical sections were used in combination with both selected staining procedures and histochemical tests to follow root development. Root surface permeability tests and the biochemical quantification of lignin were performed to complement the structural data. † Key Results The data presented suggest a redefinition of lrt1 function in lateral roots as a promoter of later development; however, neither the complete absence of lateral roots nor the frequency of their initiation is linked to lrt1 function. The developmental effects of lrt1 are under strong environmental influences. Mutant primordia are affected in structure, growth and emergence; and the majority of primordia terminate their growth during this last step, or shortly thereafter. The lateral roots are impaired in the maintenance of the root apical meristem. The primary root shows disturbances in the organization of both epidermal and subepidermal layers. The lrt1related cell-wall modifications include: lignification in peripheral layers, the deposition of polyphenolic substances and a higher activity of peroxidase. † Conclusions The present study provides novel insights into the function of the lrt1 gene in root system development. The lrt1 gene participates in the spatial distribution of initiation, but not in its frequency. Later, the development of lateral roots is strongly affected. The effect of the lrt1 mutation is not as obvious in the primary root, with no influences observed on the root apical meristem structure and maintenance; however, development of the epidermis and cortex are impaired.