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7: Embryo Development

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7 

Embryo Development

William F. Sheridan* and Janice K. Clark

Department of Biology, University of North Dakota, North Dakota, USA

7.1 Introduction

The maize embryo develops over a 40–50-day period from a single-celled zygote into a miniature plant consisting of five or six leaf primordia and a single primary root. The first detailed description of the development of the maize embryo and caryopsis, wherein it is formed, was by Randolph (1936). This was followed by an extensive report on the structure and reproduction of corn by Kiesselbach (1949). In both publications the authors utilized ink drawings and photographic images to illustrate embryo morphogenesis throughout its development. Genetic analysis of this process began early in the 20th century with the reports of Jones (1920), Demerec (1923), Mangelsdorf (1923, 1926), and Wentz (1930). Following the iconic publications of Randolph (1936) and Kiesselbach

(1949), a third descriptive paper was published by Abbe and Stein (1954). These authors introduced the terminology currently used to describe the stages of embryo development. In this chapter we describe the process of maize embryo morphogenesis and mutations that have been shown to disrupt this process.

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3: Endosperm Development and Cell Specialization

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3 

1

Endosperm Development and Cell

Specialization

Junpeng Zhan1, Joanne M. Dannenhoffer2 and Ramin Yadegari1,*

School of Plant Sciences, University of Arizona, USA; 2Department of Biology,

Central Michigan University, Michigan, USA

3.1 Introduction

The endosperm of angiosperms is a seed structure that provides nutrients and signals for embryo development and seedling germination (Li and Berger, 2012; Olsen and

Becraft, 2013). In cereal crops, it occupies the largest portion of the mature grain, contains large amounts of storage compounds including primarily carbohydrates and storage proteins, and is an important source of biofuel (Lopes and Larkins, 1993; Sabelli and Larkins, 2009; FAO, 2015). Because of its value and relatively large size, maize endosperm has become a model system for studies of endosperm development.

Angiosperm seed development is initiated by a double fertilization during which one of two sperm cells fuses with the egg cell within the female gametophyte (embryo sac) to produce the diploid embryo (1 maternal:1 paternal) and the other fertilizes the central cell to form the triploid endosperm

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2: Gametophyte Interactions Establishing Maize Kernel Development

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2 

Gametophyte Interactions Establishing

Maize Kernel Development

Erik Vollbrecht1 and Matthew M.S. Evans2,*

Department of Genetics, Development and Cell Biology, Iowa State University, USA;

2

Department of Plant Biology, Carnegie Institution for Science, Stanford, California, USA

1

2.1 Introduction

This chapter focuses on tissue- and cell-level interactions required to set in motion foundational processes that lead to and promote maize kernel development. After pollination, key cell biological, genetic, and epigenetic interactions occur, including those between the male gametophyte and the pistil, between the male and female gametophytes, and between the female gametophyte and the other seed tissues, ultimately leading to successful fertilization and initiation of kernel development (Fig. 2.1). The unicellular pollen tube germinates and grows through the transmitting tract of the silk until it reaches the ovule. It is guided by chemical cues to the ovule’s micropyle and the female gametophyte’s synergid cell. Upon interaction with the synergid, the pollen tube penetrates it and ruptures, releasing two sperm cells.

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6: Aleurone

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6 Aleurone

Bryan C. Gontarek and Philip W. Becraft*

Department of Genetics, Development and Cell Biology,

Iowa State University, Iowa, USA

6.1 Introduction

6.2  Biological Functions of Aleurone

The aleurone cell layer forms at the surface of the endosperm and is present in seeds of most flowering plants. It has epidermal-like characteristics, except that it is not directly exposed to the atmosphere; rather, it is covered by maternally derived testa and pericarp. Maize aleurone has a rich history, being instrumental in fundamental discoveries by pioneering geneticists, including

Barbara McClintock. Anthocyanin pigmentation of aleurone provides a convenient genetic marker that has led to the discovery of genes that regulate anthocyanin biosynthesis and endosperm development. Anthocyanin pigmentation in the aleurone has also been utilized to study the inheritance patterns and behaviors of genes. Transposable elements, imprinting and paramutation are among the significant discoveries facilitated by anthocyanin in the aleurone (McClintock, 1950; Brink, 1956; Kermicle, 1970). More recently, attention has focused on the aleurone per se, due to its important biological functions, implications for agronomic performance and industrial applications, and healthful properties.

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5: The Basal Endosperm Transfer Layer (BETL): Gateway to the Maize Kernel

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5   The Basal Endosperm Transfer Layer

(BETL): Gateway to the Maize Kernel

1

Prem S. Chourey1 and Gregorio Hueros2,*

U.S. Department of Agriculture, Agricultural Research Service, and

University of Florida, USA; 2Departamento de Biomedicina y

Biotecnología, Universidad de Alcalá, Madrid, Spain

5.1 Introduction

The maize basal endosperm transfer layer

(BETL), with its unique location at the juncture of maternal and filial tissues (Fig. 5.1), plays a critical role in grain-filling and defense. Symplastic discontinuity between the mother plant and BETL is elaborated through programmed cell death (PCD) in the placenta– chalaza (P–C) region. Early in development, cells in the BETL undergo structural modification through development of wall ingrowths (WIGs), which facilitate transport of sugars, nutrients, and water into the kernel. WIG development is an evolutionarily conserved trait, as it occurs in other cereal and plant species, including the maize precursor, teosinte. The BETL partitions the current and subsequent plant generation and creates an antimicrobial barrier between them with cytotoxic peptides. Our insight into the structure, function, and signaling roles of the BETL will foster future research into the development and function of this important seed tissue.

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