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Iron (Fe) toxicity is a major challenge for plant cultivation in acidic waterlogged soil environments, where lowland rice is a major staple food crop. Only few studies have addressed the molecular characterization of excess Fe tolerance in rice, and these highlight different mechanisms for Fe tolerance. Out of 16 lowland rice varieties, we identified a pair of contrasting lines, Fe-tolerant Lachit and -susceptible Hacha. The two lines differed in their physiological and morphological responses to excess Fe, including leaf growth, leaf rolling, reactive oxygen species generation and Fe and metal contents. These responses were likely due to genetic origin as they were mirrored by differential gene expression patterns, obtained through RNA sequencing, and corresponding gene ontology term enrichment in tolerant vs. susceptible lines. Thirty-five genes of the metal homeostasis category, mainly root expressed, showed differential transcriptomic profiles suggestive of an induced tolerance mechanism. Twenty-two out of these 35 metal homeostasis genes were present in selection sweep genomic regions, in breeding signatures, and/or differentiated during rice domestication. These findings suggest that Fe excess tolerance is an important trait in the domestication of lowland rice, and the identified genes may further serve to design the targeted Fe tolerance breeding of rice crops.

This work deals with the differential protein and gene expression depending from iron supply and the availability of the regulator of iron uptake in Arabidopsis thaliana, FIT (FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR), to find more FIT-regulated genes by comparison of the respective expression patterns with those of the FIT-regulated genes IRT1 and FRO2. Additionally, a possible post-transcriptional regulation of FIT is investigated to further elucidate the regulation of iron uptake in A. thaliana. Protein and RNA samples from roots of wild type plants, a fit knock-out mutant and a FIT over-expressing line have been analyzed with two-dimensional electrophoresis and CATMA v6 microarrays. Besides IRT1 and FRO2, six more FIT-regulated genes could be identified with this approach. The gene AHA2 which has been described as FIT-regulated showed a FIT-independent regulation in this work. Nine proteins have been found in distinct forms which possibly result from post-translational modification or alternative splicing, respectively. Ten more singly identified proteins displayed a post-transcriptional regulation. The investigation of a possible post-translational modification of FIT has been performed with one and two-dimensional techniques. FIT is present in at least two forms. It could be demonstrated that FIT is post-translationally modified by phosphorylation and possibly by ubiquitinylation. Diese Arbeit befasst sich mit der differenziellen Protein- und Genexpression in Abhängigkeit von der Eisenversorgung und der Verfügbarkeit des Regulators der Eisenaufnahme in A. thaliana, FIT (FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR), um durch Vergleich der Protein- und Gen-Expressionsmuster mit jenen der FIT-regulierten Gene IRT1 und FRO2 weitere von FIT regulierte Gene zu finden. Außerdem wird die posttranskriptionale Regulation von FIT untersucht, um die Regulation der Eisenaufnahme in A. thaliana weiter aufzuklären. Protein- und RNA-Proben aus Wurzeln von Wildtyp-Pflanzen, einer fit-Knock-out- und einer FIT-Überexpressionslinie wurden mit zweidimensionaler Elektrophorese sowie mit CATMA v6 Microarrays analysiert. Es konnten so neben IRT1 und FRO2 sechs weitere, FIT-regulierte Gene ermittelt werden. Das als von FIT reguliert beschriebene Gen AHA2 zeigte in dieser Arbeit eine FIT-unabhängige Regulation. Neun Proteine wurden in verschiedenen Formen gefunden, die möglicherweise das Resultat posttranslationaler Modifikation oder alternativen Splicings sind. Zehn weitere einfach identifizierte Proteine zeigten eine posttranskriptionale Regulation. Die Untersuchung einer möglichen posttranslationalen Modifikation von FIT erfolgte unter Anwendung ein- und zweidimensionaler Techniken. FIT liegt in mindestens zwei Formen vor. Es konnte gezeigt werden, dass FIT durch Phosphorylierung und möglicherweise auch durch Ubiquitinylierung posttranslational modifiziert wird.