Understanding flower development in barley (hordeum vulgare) through characterisation of multiovary mov mutants and their potential use in hybrid breeding

Abstract

In today’s world we cannot ignore the challenge of feeding an increasing global population despite more erratic and extreme weather patterns. Among the many approaches suggested to address this challenge and improve crop yield, hybrid breeding seems a promising solution. Through the phenomenon of heterosis, hybrid breeding provides the opportunity to obtain more resilient plants and more grain, thus ensuring food stability. This is particularly promising for staple crops such as wheat and rice that represent the main form of sustenance worldwide. Despite this, the application of hybrid breeding in autogamous cereals like wheat must overcome many difficulties. Specific modifications to the architecture of wheat flowers are required to maximise seed set obtained from cross-pollination, while inhibiting self-fertilization. Scientific obstacles include a complex genome organization and polyploidy, as well as the physiology and characteristics of the wheat flower itself. As a result, this project focuses on barley as a surrogate genetic model for wheat. Since barley is diploid, working with barley mutant resources greatly simplifies genetic analysis and potentially makes it easier to uncover mutant phenotypes otherwise hidden by the genic redundancy embedded within a hexaploid genome. This thesis focuses on the characterization of three barley multiovary (mov) mutants named mov1, mov2 and mov5 which show abnormal flower development. Compared to a wild-type barley floret, the mov mutants share the characteristics of having a complete or partial reduction of stamens, combined with an increase in the number of carpels. From the perspective of hybrid seed production, these mutants potentially present the dual advantage of being male-sterile and of being able to produce multiple seeds per floret. The main aims of the project were to identify which gene(s) confer the mov phenotype, understand the relationship between the identified genes and establish how the candidate genes interact with the known floral development network, particularly in the context of the ABC model. For each mutant, the approach taken relied mostly on forward genetics via mapping. Concomitantly, developmental and morphological aspects were explored using microscopy, as well as expression analysis and transient in vivo assays to determine interaction dynamics of the identified genes with known players of floral development. Overall, plausible candidate genes have been identified for each of the three mov loci and their role in flower development has been explained. These results provide the basis for a model explaining flower development in barley, taking into account not only the main genetic actors, but also their regulators. The knowledge transfer from barley to wheat and the applicability of using floral development mutants for wheat hybrid breeding is discussed.