Acclimation to elevated CO2 is improved by low Rubisco and carbohydrate content, and enhanced Rubisco transcripts in the G132 barley mutant

Variations induced by mutagenesis may identify targets for adapting to rising atmospheric CO2concentrations. G132 is a barley (Hordeum vulgare L.) mutant with strong decreases in photosynthesis,Rubisco and carbohydrate content, but increased Rubisco transcripts. We tested the hypothesis that G132will record a greater stimulation of photosynthesis and dry mass gain than the wild-type (WT) in responseto CO2 enrichment. A growth chamber experiment compared the mutant G132 and the Graphic WTdeveloped in ambient (390 μmol mol-1) and elevated (1200 μmol mol-1) CO2. Photosynthesis, protein andcarbohydrate contents, plant dry matter and leaf area were determined. The transcriptome responses toelevated CO2 were investigated using microarrays and qRT-PCR. CO2 enrichment increased leaf area inG132 but not in WT, and induced greater dry mass increases in the mutant, attributable to increases in totalgreen area in the former. Growth in elevated CO2 stimulated photosynthesis more in G132 than in WT, inassociation with a lack of Rubisco down-regulation and lower carbohydrate levels in G132. Elevated CO2induced more changes in gene expression in WT than G132. Clustering of the corresponding transcriptsshowed that the expression of genes involved in carbohydrate synthesis, in G132, cell wall synthesis andmodification, in WT, nitrate reductase, significantly more in G132 than WT, and jasmonate metabolism inG132 was enhanced, while that for stress-related genes was repressed in both genotypes by elevated CO2.Rising atmospheric CO2 decreased the transcript levels for a greater number of transcription factors in WTthan in G132. The low Rubisco and carbohydrate content and enhanced Rubisco transcripts recorded inG132 are traits that may improve adaptation to elevated CO2.