485 I. 485 II. 486 III. 491 IV. 491 V. 495 495 References 495 SUMMARY: Boundaries, established and maintained in different regions of the plant body, have diverse functions in development. One role ...is to separate different cell groups, for example the differentiating cells of a leaf primordium from the pluripotent cells of the apical meristem. Boundary zones are also established during compound leaf development, to separate young leaflets from each other, and in many other positions of the plant body. Recent studies have demonstrated that different boundary zones share similar properties. They are characterized by a low rate of cell divisions and specific patterns of gene expression. In addition, the levels of the plant hormones auxin and brassinosteroids are down‐regulated in boundary zones, resulting in a low differentiation level of boundary cells. This feature seems to be crucial for a second important role of boundary zones, the formation of new meristems. The primary shoot meristem, as well as secondary and ectopic shoot meristems, initiate from boundary cells that exhibit competence for meristem formation.
Leaf shape varies markedly. Here I focus on the diversity in leaf contour, which can be considered marginal variation in curvature if we omit detailed marginal structures such as serrations. This ...curvature can be described by a combination of sigmoids: a curve for the apical half and a curve for the basal half connected with or without an interval. Marginal curvature is determined by the position of the leaf meristem, the acceleration and deceleration of cell proliferation in the leaf meristem, and the angle of directed cell proliferation. Several key factors contributing to this variation have been revealed to date, but the majority of the underlying genetic mechanisms are unclear. Here I provide an overview of current knowledge and propose future directions for the field.
We review developmental transitions of rice shoot meristems to branched inflorescences with floral meristems, highlighting evolutionarily conserved regulators and factors with distinct functions in ...shoot architecture and reproductive development.
Abstract
Grasses have evolved complex inflorescences, where the primary unit is the specialized short branch called a spikelet. Detailed studies of the cumulative action of the genetic regulators that direct the progressive change in axillary meristem identity and their terminal differentiation are crucial to understanding the complexities of the inflorescence and the development of a determinate floret. Grass florets also pose interesting questions concerning the morphologies and functions of organs as compared to other monocots and eudicots. In this review, we summarize our current knowledge of the regulation of the transitions that occur in grass inflorescence meristems, and of the specification of floret meristems and their determinate development. We primarily use rice as a model, with appropriate comparisons to other crop models and to the extensively studied eudicot Arabidopsis. The role of MADS-domain transcription factors in floral organ patterning is well documented in many eudicots and in grasses. However, there is evidence to suggest that some of these rice floral regulators have evolved distinctive functions and that other grass species-specific factors and regulatory pathways occur - for example the LOFSEP 'E' class genes OsMADS1 and OsMAD34, and ramosa genes. A better understanding of these systems and the epigenetic regulators and hormone signaling pathways that interact with them will provide new insights into the rice inflorescence meristem and the differentiation of its floret organs, and should indicate genetic tools that can be used to control yield-related traits in both rice and other cereal crops.
Genetic Regulation of Shoot Architecture Wang, Bing; Smith, Steven M; Li, Jiayang
Annual review of plant biology,
04/2018, Letnik:
69, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Shoot architecture is determined by the organization and activities of apical, axillary, intercalary, secondary, and inflorescence meristems and by the subsequent development of stems, leaves, shoot ...branches, and inflorescences. In this review, we discuss the unifying principles of hormonal and genetic control of shoot architecture including advances in our understanding of lateral branch outgrowth; control of stem elongation, thickness, and angle; and regulation of inflorescence development. We focus on recent progress made mainly in
Arabidopsis thaliana
, rice, pea, maize, and tomato, including the identification of new genes and mechanisms controlling shoot architecture. Key advances include elucidation of mechanisms by which strigolactones, auxins, and genes such as
IDEAL PLANT ARCHITECTURE1
and
TEOSINTE BRANCHED1
control shoot architecture. Knowledge now available provides a foundation for rational approaches to crop breeding and the generation of ideotypes with defined architectural features to improve performance and productivity.
The forms resulting from growth processes are highly sensitive to the nature of the driving impetus, and to the local properties of the medium, in particular, its isotropy or anisotropy. In turn, ...these local properties can be organized by growth. Here, we consider a growing plant tissue, the shoot apical meristem of Arabidopsis thaliana. In plants, the resistance of the cell wall to the growing internal turgor pressure is the main factor shaping the cells and the tissues. It is well established that the physical properties of the walls depend on the oriented deposition of the cellulose microfibrils in the extracellular matrix or cell wall; this order is correlated to the highly oriented cortical array of microtubules attached to the inner side of the plasma membrane. We used oryzalin to depolymerize microtubules and analyzed its influence on the growing meristem. This had no short-term effect, but it had a profound impact on the cell anisotropy and the resulting tissue growth. The geometry of the cells became similar to that of bubbles in a soap froth. At a multicellular scale, this switch to a local isotropy induced growth into spherical structures. A theoretical model is presented in which a cellular structure grows through the plastic yielding of its walls under turgor pressure. The simulations reproduce the geometrical properties of a normal tissue if cell division is included. If not, a "cell froth" very similar to that observed experimentally is obtained. Our results suggest strong physical constraints on the mechanisms of growth regulation.
The astonishingly long lives of plants and their regeneration capacity depend on the activity of plant stem cells. As in animals, stem cells reside in stem cell niches, which produce signals that ...regulate the balance between self-renewal and the generation of daughter cells that differentiate into new tissues. Plant stem cell niches are located within the meristems, which are organized structures that are responsible for most post-embryonic development. The continuous organ production that is characteristic of plant growth requires a robust regulatory network to keep the balance between pluripotent stem cells and differentiating progeny. Components of this network have now been elucidated and provide a unique opportunity for comparing strategies that were developed in the animal and plant kingdoms, which underlie the logic of stem cell behaviour.
The growing apices of plants contain stem cells that continually produce tissues, which, in the shoot, include the germline. These stem cell populations remain active throughout the plant's life, ...which can last for centuries, and are particularly exposed to environmental hazards that cause DNA damage and mutations. It is not known whether plants have mechanisms to safeguard the genome specifically in these crucial cell populations. Here, we show that root and shoot stem cells and their early descendants are selectively killed by mild treatment with radiomimetic drugs, x-rays, or mutations that disrupt DNA repair by nonhomologous end-joining. Stem cell death required transduction of DNA damage signals by the ATAXIA-TELANGIECTASIA MUTATED (ATM) kinase and, specifically in the root, also the ATM/RAD3-RELATED (ATR) kinase. Consistent with the absence of p53 and the core apoptotic machinery in plants, death of the stem cells did not show apoptotic but autolytic features as seen in other cases of plant developmentally programmed cell death. We propose that plants have independently evolved selective death as a stringent mechanism to safeguard genome integrity in their stem cell populations.
Heterotrimeric G proteins are important transducers of receptor signaling, functioning in plants with CLAVATA receptors in controlling shoot meristem size and with pathogen-associated molecular ...pattern receptors in basal immunity. However, whether specific members of the heterotrimeric complex potentiate crosstalk between development and defense, and the extent to which these functions are conserved across species, have not yet been addressed. Here we used CRISPR/Cas9 to knock out the maize G protein β subunit gene (Gβ) and found that the mutants are lethal, differing from those in Arabidopsis, in which homologous mutants have normal growth and fertility. We show that lethality is caused not by a specific developmental arrest, but by autoimmunity. We used a genetic diversity screen to suppress the lethal Gβ phenotype and also identified a maize Gβ allele with weak autoimmune responses but strong development phenotypes. Using these tools, we show that Gβ controls meristem size in maize, acting epistatically with G protein α subunit gene (Gα), suggesting that Gβ and Gα function in a common signaling complex. Furthermore, we used an association study to show that natural variation in Gβ influences maize kernel row number, an important agronomic trait. Our results demonstrate the dual role of Gβ in immunity and development in a cereal crop and suggest that it functions in cross-talk between these competing signaling networks. Therefore, modification of Gβ has the potential to optimize the trade-off between growth and defense signaling to improve agronomic production.
Grass flowers are organized on small branches known as spikelets. In maize, the spikelet meristem is determinate, producing one floral meristem and then converting into a second floral meristem. The ...APETALA2 (AP2)-like gene indeterminate spikelet1 (ids1) is required for the timely conversion of the spikelet meristem into the floral meristem. Ectopic expression of ids1 in the tassel, resulting from a failure of regulation by the tasselseed4 microRNA, causes feminization and the formation of extra floral meristems. Here we show that ids1 and the related gene, sister of indeterminate spikelet1 (sid1), play multiple roles in inflorescence architecture in maize. Both genes are needed for branching of the inflorescence meristem, to initiate floral meristems and to control spikelet meristem determinacy. We show that reducing the levels of ids1 and sid1 fully suppresses the tasselseed4 phenotype, suggesting that these genes are major targets of this microRNA. Finally, sid1 and ids1 repress AGAMOUS-like MADS-box transcription factors within the lateral organs of the spikelet, similar to the function of AP2 in Arabidopsis, where it is required for floral organ fate. Thus, although the targets of the AP2 genes are conserved between maize and Arabidopsis, the genes themselves have adopted novel meristem functions in monocots.
Auxin and above-ground meristems Wang, Ying; Jiao, Yuling
Journal of experimental botany,
01/2018, Letnik:
69, Številka:
2
Journal Article
Recenzirano
Odprti dostop
This review summarizes recent findings on auxin regulation of the shoot apical meristem, axillary meristem, floral meristem, and adventitious meristem.
Abstract
In contrast to animals, plants ...maintain life-long post-embryonic organogenesis from specialized tissues termed meristems. Shoot meristems give rise to all aerial tissues and are precisely regulated to balance stem cell renewal and differentiation. The phytohormone auxin has a dynamic and differential distribution within shoot meristems and during shoot meristem formation. Polar auxin transport and local auxin biosynthesis lead to auxin maxima and minima to direct cell fate specification, which are critical for meristem formation, lateral organ formation, and lateral organ patterning. In recent years, feedback regulatory loops of auxin transport and signaling have emerged as major determinants of the self-organizing properties of shoot meristems. Systems biology approaches, which involve molecular genetics, live imaging, and computational modeling, have become increasingly important to unravel the function of auxin signaling in shoot meristems.
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