MOLECULAR DESIGN OF A NOVEL DUAL-PURPOSE BARLEY VARIETY

By mid-century the bio-based economy is expected to have grown significantly in Europe and all around the world. A pillar of this, both now and in the future, is the sustainable processing of biomass into a spectrum of marketable products and energy. That will depend largely on the availability of a reliable supply of appropriate quantities of biomass in a sustainable manner and at fair prices. Among the primary sources of agriculture-derived biomass, crop residues have a great potential to supply large, reliable, and sustainable quantities of biomass. This Ph.D. thesis work was aimed to address this issue using barley as model crop, since its straw is characterized by the largest content of carbohydrates among cereals, thus a valuable product for its potential conversion into biofuels and other eco-friendly products. Especially, we tried to explore the possibility to increase barley biomass production, without penalty on grain yield, by improving the light phase of photosynthesis through: i) decreasing the light harvesting antenna size of photosystems, thus reducing the excess of light absorption on top of the canopy, together with the consequent decrease in photo-damage, and favoring a more uniform light absorption and photosynthesis throughout the canopy; ii) the fine-tuning of the photoprotective mechanism, known as Non-Photochemical Quenching mechanism (NPQ), with aim to have a more rapid induction/relaxation of this mechanism, hence a better photosynthetic performance. Within this frame, we have characterised into details the hus1 (happy under the sun) barley mutant, isolated by a forward genetics approach within the HorTILLUS chemical mutagenize population. hus1 plants are characterised by pale-green leaves, a reduced antenna size of photosystems and an improved photosynthetic performance with respect to cv. Sebastian, used as control. Segregation analysis performed on the F2 population obtained by crossing hus1 with Morex indicates that the hus1 phenotype is caused by a monogenic recessive allele. Using exome capture sequencing of DNA pools from 50 WT and 50 hus1-like plants, the putative SNP mutation has been identified in the Arabidopsis thaliana homologous CHAOS gene, encoding the Chloroplast Signal Recognition Particle 43 (cpSRP43), a stromal chaperone that upload the antenna proteins into the thylakoid membranes. As a matter of fact, immune-blot analyses confirmed that barley hus1 and the Arabidopsis chaos mutants have a similar reduction in the levels of antenna protein accumulation. Furthermore, using an allele mining strategy, the natural genetic variability of HUS1 locus has been studied in the exome sequences of the Whealbi collection. 26 accessions with different polymorphisms have been identified in HUS1 locus. A preliminary screening led to the identification of few pale lines that seem to have a higher photosynthetic activity compared to the corresponding WT. These natural accessions have been collected from different regions of the planet and represent an invaluable genetic material to understand how photosynthesis adapt to the different growth conditions. With respect to fine-tuning of NPQ, a reverse genetic approach has been used to identify allelic variants of Violaxanthin De-Epoxidase (VDE) and Zeaxanthin Epoxidase (ZEP) enzymes both involved in the xanthophyll cycle, an integral part of NPQ photoprotective mechanism. Five allelic variants of the VDE gene and one of ZEP gene have been found. Most of the mutant plants show a Sebastian-like phenotype under green-house growth conditions, but they show very different NPQ kinetics, thus representing the ideal genetic material to investigate the impact of NPQ alteration on photosynthetic performance and biomass accumulation.