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Title:Improving C4 photosynthetic chilling tolerance in bioenergy crops: the search for elite breeding materials
Author(s):Spitz, Idan
Advisor(s):Long, Stephen
Department / Program:Plant Biology
Discipline:Plant Biology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):bioenergy crop
cold tolerance
Miscanthus x giganteus
plant breeding
Saccharum spontaneum
frost tolerance
Abstract:Increasing global energy demands and geopolitical instability among the world’s major fossil fuel-producing countries have created an increased interest in alternative energy sources, particularly for liquid transportation fuels. Among these sources for alternative energy are biofuels, which entail the utilization of plant-based starch, sugar, oil, and potentially lignocellulosic biomass in the production of fuels. Due to their high productivity, C4 bioenergy feedstocks are among the top candidates for cultivation for biomass production, and crops such as sugarcane/energycane (Saccharum spp.), maize (Zea mays) , miscanthus (Miscanthus spp.), sorghum (Sorghum bicolor), and switchgrass (Panicum virgatum) have been suggested for the production of lignocellulosic biomass for bio-ethanol production. Under optimal conditions these C4 plants produce high biomass yields and have higher water and nitrogen use efficiencies than plants utilizing the C3 photosynthetic pathway, although these advantages are only seldom realized under suboptimal temperatures due to photosynthetic limitations at chilling temperatures (<20° C). The mechanistic limitation at chilling temperatures has been suggested to be caused by the chilling-induced lability of pyruvate phosphate dikinase (PPDK) and decrease in ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) enzyme contents, which directly limits the C4 cycle and indirectly leads to damage to the photosynthetic apparatus in the thylakoid membrane and generate harmful reactive oxygen species further downstream. The bioenergy feedstock Miscanthus x giganteus is a leading candidate for biomass production in high latitudes of N. America, Europe, and Asia due to its high biomass yields and photosynthetic tolerance of mild chilling temperatures (15-20° C). However, Miscanthus x giganteus lacks tolerance of severe chilling conditions (0–12° C) and overnight frosts associated with early-season days in high latitudes. In chapter 2, two species from the Miscanthus genus are evaluated for their tolerance of severe chilling and overnight frost in the first comprehensive screening of a Siberian Miscanthus sacchariflorus germplasm collection. The objective here was to identify Miscanthus germplasm with superior tolerance of severe chilling and frost than those of Miscanthus x giganteus. One Miscanthus sacchariflorus accession was found to have higher photosynthetic chilling tolerance over a 15-day chilling period, and maintained higher net rate of carbon assimilation and quantum yield of photosystem II over the chilling period and on return to moderate temperature, while Miscanthus x giganteus maintained the highest rates of leaf elongation throughout the chilling treatment. Additionally, all Miscanthus sacchariflorus accessions showed comparable tolerance of overnight frost to that of Miscanthus x giganteus. Energycane is a bioenergy feedstock candidate for biomass production in warm temperate and subtropical climates of the United States but photosynthetic limitations of the C4 cycle at suboptimal temperatures have limited the range at which it can be optimally cultivated, and the development of chilling-tolerant varieties is essential for extension of the growing season and mitigation of losses to biomass yields at higher latitudes. In chapter 3, I present an early-generation testing of the photosynthetic chilling tolerance of mild chilling temperatures in twenty six energycane hybrids generated from 10 crosses by the USDA-ARS basic breeding program in Houma, LA. The objective of this study is an early-generation screening of Saccharum spp. and inter-generic hybrids for Saccharum for superior photosynthetic chilling tolerance. The majority of energycane genotypes investigated here showed higher or comparable chilling tolerance than the chilling-intolerant S. officinarum ‘LA Purple’, while three energycane F1 hybrids (HB07-3452-4, HB07-3073-6, and HB07-3329-5) maintained the highest rates of leaf carbon assimilation over the chilling period and on return to moderate temperature. The results presented in this thesis show that opportunity exists in wild germplasm material for the improvement of chilling tolerance in Miscanthus x giganteus, and that superior chilling tolerance can be generated in energycane through inter-specific and inter-generic crosses. In Miscanthus and energycane, severe chilling (10° C) and moderate chilling (15° C), respectively reduced the capacity for recovery under chilling conditions. Maintenance of photosynthetic capacity under chilling conditions and recovery at re-elevated temperatures are suggested here to be a function of regulation of specific enzymes involved in the C4 cycle, maintenance of thylakoid membrane proteins, light-energy dissipation strategies, generation of alternate electron sinks, and reactive oxygen scavenging.
Issue Date:2015-12-10
Rights Information:Copyright 2015 Idan Spitz
Date Available in IDEALS:2016-03-02
Date Deposited:2015-12

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