| Summary: | Ferrochelatase (FC) is the terminal enzyme of heme biosynthesis. In photosynthetic organisms studied so far, there is evidence for two FC isoforms, which are encoded by two genes (<i>FC1</i> and <i>FC2</i>). Previous studies suggest that these two genes are required for the production of two physiologically distinct heme pools with only <i>FC2</i>-derived heme involved in photosynthesis. We characterised two <i>FC</i>s in barley (<i>Hordeum vulgare</i> L.). The two HvFC isoforms share a common catalytic domain, but HvFC2 additionally contains a C-terminal chlorophyll a/b binding (CAB) domain. Both <i>HvFC</i>s are highly expressed in photosynthetic tissues, with <i>HvFC1</i> transcripts also being abundant in non-photosynthetic tissues. To determine whether these isoforms differentially affect photosynthesis, transgenic barley ectopically overexpressing <i>HvFC1</i> and <i>HvFC2</i> were generated and evaluated for photosynthetic performance. In each case, transgenics exhibited improved photosynthetic rate (<i>A</i><sub>sat</sub>), stomatal conductance (<i>g</i><sub>s</sub>) and carboxylation efficiency (CE), showing that both <i>FC1</i> and <i>FC2</i> play important roles in photosynthesis. Our finding that modified <i>FC</i> expression can improve photosynthesis up to ~13% under controlled growth conditions now requires further research to determine if this can be translated to improved yield performance under field conditions.
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