Investigation of male reproductive traits of agronomic importance in cereals

Male fertility in flower development is important for breeding and yield stability in cereals. An intricate gene regulatory network in close association with environmental cues are required for formation of viable pollen and timely release of pollen from the anther. Hybrid breeding, the crossing of two elite cultivars, have the potential of generating varieties with increased yield and resistance to abiotic stresses but for crossing of elite parents for large scale seed production, certain qualities are required. The male parent should have high pollen production and effective dispersal whereas the female parent needs to exhibit male sterility to prevent self-pollination and be receptive of non-self pollen. In this project the impact of male traits on fertility and pollen dispersal have been studied in cereals to enhance understanding of processes useful for hybrid breeding. Three separate studies were carried out using forward and reverse genetic approaches to study traits related to male fertility and its effect on yield and traits of agronomic importance. In addition, anther development in angiosperm flowers was reviewed in an evolutionary perspective. Abiotic stresses such as cold stress can severely affect floral development and lead to yield losses due to inhibited plant growth or flowering. However, there is limited knowledge of how genes involved with pollen development in cereals are connected to abiotic stress management processes under cold and drought stress. Here, a putative orthologue of the Arabidopsis INDUCER OF CBF EXPRESSION1 (ICE1) was identified and investigated in barley in relation to yield and stomatal formation under cold and drought stress. Vectors carrying CRISPR/Cas9 single guide RNA (sgRNA) targets, HvICE1-1 overexpression or HvICE1-1 silencing constructs were transformed into barley to study the gene in planta. The overexpression of HvICE1-1 was found to reduce the induction of the downstream HvCBF3 after freezing stress, a process which is critical for cold response, as well as reduce yield due to inhibited plant growth, whereas silencing of HvICE1-1 interfered with the formation of stomata on the leaf surface. HvICE1-1 was further shown to influence the photosynthetic capacity of the plant suggesting that the putative HvICE1 orthologue is involved with a diverse set of processes in plant development and physiology. Anther traits were investigated in hexaploid wheat to study the genetic component of these traits. To identify quantitative trait loci (QTLs) controlling anther length and anther extrusion in wheat, three populations with varying degree of genetic diversity were phenotyped and used for genome wide association studies (GWA studies). In total 427 elite wheat cultivars, 95 wild wheat introgression lines, and a bi-parental mapping population with 475 plants were used to identify 11 and 6 loci potentially involved with the regulation of anther length and extrusion. Heritability was found to be high for anther extrusion and anther length in all populations with a medium correlation between anther extrusion and plant height. Finally, underlying loci involved with genic male sterility were studied in barley using a collection of male sterile barley mutants. The lines were genotyped with a high density 35k SNP array to identify regions of interest and to enable future fine-mapping of loci of interest. Together these studies of male fertility in cereal flowers and the effect of abiotic stresses on yield have increased the understanding of cereal floral biology to enable future hybrid breeding