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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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16: Natural Variations in Maize Kernel Size: A Resource for Discovering Biological Mechanisms

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16 

Natural Variations in Maize Kernel Size:

A Resource for Discovering Biological

Mechanisms

1

Xia Zhang1 and Shawn K. Kaeppler2,*

Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing,

China; 2Department of Agronomy and Great Lakes Bioenergy Research Center,

University of Wisconsin, Madison, Wisconsin, USA

16.1 Introduction

Seed size is a trait that has been selected during the domestication and improvement of multiple crop species. In maize, the caryopsis or kernel is a fruit composed of the maternal pericarp surrounding the zygotic seed tissues. Kernel size increased dramatically during the domestication of maize (Zea mays ssp. mays) from its wild progenitor, teosinte (Zea mays ssp. parviglumis) (Doebley and Stec, 1993). Today, maize is one of the most important crops worldwide, providing food for human consumption, feed for livestock, and raw materials for industrial products. Given the increasing size of the human population and concomitant demand for food and renewable resources, crop scientists are striving to increase the productivity and sustainability of maize and other primary agricultural crops. Yield components, such as kernel size, are among targets to increase yield potential in maize. In industrialized countries, maize kernel size and shape are of great consequence to growers because of their relevance to mechanized cultivation, harvesting, and processing.

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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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4: What Can We Learn from Maize Kernel Mutants?

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4 

What Can We Learn from Maize

Kernel Mutants?

Donald R. McCarty*

Department of Horticultural Sciences, University of Florida, USA

4.1 Introduction

Maize kernel mutants have provided insight into the mechanisms of embryo and endosperm formation for more than a century

(Neuffer and Sheridan, 1980; Sheridan and

Neuffer, 1980; Clark and Sheridan 1991; Sheridan and Clark, 1993). Advances in genomics technologies revolutionized our ability to learn from them, and recent application of transposon mutagenesis enabled their genome-wide analysis (McCarty et al., 2005,

2013; Hunter et al., 2014). With current gene discovery and genome editing technologies, there is no longer a distinction between forward and reverse genetics approaches to linking genes and phenotypes. Moreover, genetic and phenotypic analyses can be integrated with other types of genomic data that place genes in networks, providing even deeper insight into their functions.

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