Abstract:
The atmospheric Carbon Dioxide concentration ([CO2]) is"'increasing at a significant rate and predicted to reach up to 700 µmo! mo!-1 by the end of this century. Elevated [CO2] significantly promotes the growth of most C3 crops through increased photosynthesis capacity and reduced stomata! conductance. This stimulation of photosynthesis is central to other post-photosynthetic key metabolic processes such as Carbon and Nitrogen metabolism, cell cycle functions and hormonal regulation, which may lead to change the entire plant growth. The CO2 responsiveness of crops varies among genotypes and more pronounced in the early development stages. However, the underlying molecular mechanisms by which elevated [CO2] alter growth responses which are not clearly understood yet. Therefore, this study broadly aimed to dissect the molecular mechanisms of plant growth responses to elevated [CO2] in wheat (Triticum aestivum L.), focusing on the early vegetative stage. First, putative Quantitative Trait Loci (QTL) for major early growth traits were identified using a doubled haploid mapping population of a cross between RAC875 and Kukri grown at either ambient ( 400 µmo! moJ-1) or elevated [CO2] (700 µmo! mol·1). In total, 24 putative QTL for CO2 responsiveness were identified for different growth traits. Secondly, physiological and molecular approaches were employed to understand the impact of photosynthesis and post-photosynthetic metabolic processes on plant growth responses at elevated [CO2]. Transcript abundance of key genes involved in Carbon and Nitrogen metabolism, and cell cycle functions varied greatly among CO2 levels (400 and 700 µmol moP), organ types (last fully expanded leaves, expanding leaves, leaf cell elongation zone and shoot apex region) and genotypes. Finally, the interplay of different regulatory mechanisms involved in plant growth at elevated [CO2] was investigated through a comparative proteomics analysis. Most of the differentially expressed proteins at elevated [CO2] were involved in Carbon metabolism, energy pathways, protein synthesis, and cell cycle functions. Overall, the results indicated that post-photosynthetic metabolic processes play a significant role in moderating plant growth responses at elevated [CO2].
