Flower fertility in barley: how to make more seeds

Have you ever been to a barley or wheat field? From a far distance, all plants look alike. However, if you look closer you might notice that they can look quite different from each other: different plant height, leaf number, spike size, or even seed number within one spike. This variation can arise from environmental factors, such as light intensity or temperature, and/or from genetic variation. Variation in seed number is of particular interest given the high agronomic importance of seeds. As wheat and barley are amongst the most important cereals in agriculture, increasing their yield is crucial to ensure food security. Early in development cereals initiate a large number of flowers that may ultimately develop into seeds. However, only a certain proportion of those flowers develop and become fertile. The reasons why some abort and others survive and develop into seeds is not yet fully understood. A better understanding of the factors that determine seed number is crucial and could enhance the efficiency of breeding programs aimed at improving grain yield. My project within CEPLAS aims at understanding the genetic and environmental factors that regulate the flower fertility in barley.

The flowers of cereals are specialized short branches formed on opposite sides of the central rachis of the spike, where ultimately pollination takes place and a seed is formed (Figure 1). Flower development occurs during the reproductive development phase of the life cycle, and comprises two major developmental transitions: first, flower primordia are initiated; after that, they begin to develop and floral development starts. Several weeks may pass between the initiation of the first flower primordia and pollination. Recent studies in cereals have suggested that the later phase of development controls flower survival and abortion, and is strongly affected by environmental conditions and nutrient availability. Flower survival is thus far more relevant than flower initiation in the determination of the final number of seeds.

The major positive regulators of flowering in barley are the genes PHOTOPERIOD 1 (Ppd-H1) and FLOWERING LOCUS T 1 (FT1). Ppd-H1 controls the timing of flowering and maturity, and also plays an important role in flower fertility and seed set. So far, FT-like genes in cereal monocots have only been described as central regulators of the transition from vegetative to reproductive growth. However, the hypothesis that they have a role in determining flower formation and fertility is gaining a new body of evidence.
To explore this hypothesis, we generated a mutant population and selected lines with mutations in the genes Ppd-H1, FT1, and FT2. These lines were grown in the field with the wild-type control Antonella, and the spike fertility was scored. We observed that the number of seeds per spike is strongly reduced in the mutant lines when compared to the wild-type Antonella (Figure 2). The ft1 mutants have the most striking spike phenotype. The spikes of the ppd-h1 mutant are apparently normal, but a closer look reveals that many seeds are empty. Based on these phenotypes, it seems likely that the mutated genes are important for fertility. I am currently investigating the cause for the reduced fertility, and ultimately I want to identify the role that the FT1, FT2, and Ppd-H1 genes play in this process.

Food security is one of the major societal challenges we are facing today because the current supply will not be able to cope with the predicted increasing demand in the coming years. The supply is highly dependent on a wide variety of factors that include an adequate climate, available arable land, water availability, high yielding crops, and good distribution chains. Meeting the challenges of our future food chain involves everyone across the food system. The role of scientists in this process should not be underestimated: bringing innovation and increased knowledge can contribute to solving agricultural problems in a sustainable fashion. 

Dr. Filipa Tomé, Max Planck Institute for Plant Breeding Research, Cologne

Planter’s Punch

Under the heading Planter’s Punch we present each month one special aspect of the CEPLAS research programme. All contributions are prepared by our young researchers.

Further Reading

Leonard Gol*, Filipa Tomé*, Maria von Korff (2017) Floral transitions in wheat and barley: interactions between photoperiod, abiotic stresses, and nutrient status. J Exp Bot 2017; 68 (7): 1399-1410

About the Author

The article was written by Filipa Tomé, who is a member of the CEPLAS Postdoc Programme. She aims to understand the genetic and environmental factors that regulate flower fertility in barley. With her research she wants to contribute to the rising global food demand.

Heinrich Heine University
University of Cologne
Max Planck Institute for Plant Breeding Research
Forschungszentrum Jülich