Natural Variation in Ovule Morphology Is Influenced by Multiple Tissues and Impacts Downstream Grain Development in Barley (Hordeum vulgare L.).

Laura G Wilkinson,Rachel A Burton,Xiujuan Yang,Matthew R Tucker,Tobias Würschum

doi:10.3389/fpls.2019.01374

Laura G Wilkinson, Rachel A Burton + Show 3 more

Open Access

https://doi.org/10.3389/fpls.2019.01374

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Abstract

The ovule plays a critical role in cereal yield as it is the site of fertilization and the progenitor of the grain. The ovule primordium is generally comprised of three domains, the funiculus, chalaza, and nucellus, which give rise to distinct tissues including the integuments, nucellar projection, and embryo sac. The size and arrangement of these domains varies significantly between model eudicots, such as Arabidopsis thaliana, and agriculturally important monocotyledonous cereal species, such as Hordeum vulgare (barley). However, the amount of variation in ovule development among genotypes of a single species, and its functional significance, remains unclear. To address this, wholemount clearing was used to examine the details of ovule development in barley. Nine sporophytic and gametophytic features were examined at ovule maturity in a panel of 150 European two-row spring barley genotypes, and compared with grain traits from the preceding and same generation. Correlations were identified between ovule traits and features of grain they produced, which in general highlighted a negative correlation between nucellus area, ovule area, and grain weight. We speculate that the amount of ovule tissue, particularly the size of the nucellus, may affect the timing of maternal resource allocation to the fertilized embryo sac, thereby influencing subsequent grain development.

Highlights

Barley is a cereal that has sustained humans for thousands of years and remains a crop of key agricultural and economic importance (Samuel 1996; Eitam et al, 2015)
This series of ovule stages from Ov2 to Ov10 is equivalent to the phase of barley pistil development represented by stages W6 to W10 on the Waddington scale (Figure S2)
This study examined the range of natural variation present in mature ovule phenotypes among a population of two-row spring barleys

Summary

Introduction

Barley is a cereal that has sustained humans for thousands of years and remains a crop of key agricultural and economic importance (Samuel 1996; Eitam et al, 2015). All of the organs and tissues required for self-fertilization and seed production are located within this floret. This includes a single ovule within a single ovary (pistil), which together comprise the female reproductive organs that give rise to and protect the bulk of the tissues within the grain. Heat and drought stress have been shown to compromise aspects of pistil and ovule maturation, leading to defects in fertilization and grain development in wheat (Triticum aestivum) and maize (Zea mays; (Saini et al, 1983; Jäger et al, 2008; Oury et al, 2016; Onyemaobi et al, 2018). Correct development of the female reproductive organs is an important determinant of floral fertility and yield, especially under conditions of environmental stress. A greater understanding of ovule and pistil development in cereal crops may provide breeding targets for improved yield and yield stability

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