Identification and Expression Analysis of Multiple Ferric Chelate Reductases in Citrus junos

Abstract

<jats:p>Ferric chelate reductase (FRO) is a critical enzyme for iron absorption in strategy I plants, reducing Fe<jats:sup>3+</jats:sup> to Fe<jats:sup>2+</jats:sup>. To identify <jats:italic>FRO</jats:italic> family genes in the local <jats:italic>Citrus junos</jats:italic> cultivar Ziyang Xiangcheng and to reveal their expression model, the citrus (<jats:italic>Citrus</jats:italic> sp.) genome was searched for homologies of the published sequence <jats:italic>CjFRO1</jats:italic>. Five <jats:italic>FRO</jats:italic>s were found, including <jats:italic>CjFRO1</jats:italic>; these were named <jats:italic>CjFRO2</jats:italic>, <jats:italic>CjFRO3</jats:italic>, <jats:italic>CjFRO4</jats:italic>, and <jats:italic>CjFRO5</jats:italic>, respectively, and cloned via reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) PCR. The deduced amino acid sequences of five <jats:italic>CjFRO</jats:italic>s contained flavin adenine dinucleotide (FAD)-binding motifs, nicotinamide adenine dinucleotide (NAD)-binding motifs, and 6–10 transmembrane domains, with isoelectric points between 6.73 and 9.46, and molecular weights between 67.2 and 79.9 kD. <jats:italic>CjFRO1</jats:italic> and <jats:italic>CjFRO2</jats:italic> were predominantly found in the aboveground parts of <jats:italic>C. junos</jats:italic>, with <jats:italic>CjFRO1</jats:italic> highly expressed in leaves, and <jats:italic>CjFRO2</jats:italic> largely expressed in stems and leaves. <jats:italic>CjFRO3</jats:italic> was less expressed in roots, stems, and leaves. <jats:italic>CjFRO4</jats:italic> and <jats:italic>CjFRO5</jats:italic> were predominately found in roots. Under iron-deficient conditions, <jats:italic>CjFRO4</jats:italic> was significantly and specifically increased in the roots of <jats:italic>C. junos</jats:italic>, whereas <jats:italic>CjFRO1</jats:italic> was upregulated in the roots and leaves.</jats:p>