Understanding the role of metal homeostasis related candidate genes in Fe/Zn uptake, transport and redistribution in rice using semi-quantitative RT-PCR

Abstract

Expression of twenty five metal transport related genes was analyzed in root and leaf tissue of twelve diverse rice genotypes at maximum tillering (MTS) and mid-grain fill (MGF) stages to understand their role in iron/zinc uptake and transport and remobilization. Well-nourished rice plants grown with sufficient supply of iron (Fe) and zinc (Zn) were used for expression analysis. Differential expression of metal homeostasis related candidate genes was observed among genotypes, tissue types and developmental stages. Maximum number of genes (twenty four) genes expressed in flag leaf tissue (MGF) showing variation in level of expression among genotypes. Root transcriptome profiling revealed that nine genes (OsZIP4, OsZIP11, OsNRAMP5, OsNRAMP7, OsYSL2, OsYSL4, OsYSL6, OsYSL9, OsNAAT1 and OsNAC) expressed at both developmental stages (MGF and MTS), three genes (OsFER1, OsVIT1 and OsFRO2) expressed at MTS only while seven genes (OsIRT1, OsFER2, OsZIP7, OsZIP8, OsZIP9, OsNRAMP4, OsNRAMP6 and OsYSL12) expressed at MGF stage only. Rest of the five genes showed either poor or negligible expression in root tissue of all studied rice genotypes at both the developmental stages. Characterization of rice leaf transcriptome at MTS revealed negligible or poor level of expression of eleven genes (OsFER2, OsIRT1, OsNAS2, OsYSL12, OsYSL17, OsNRAMP4, OsNRAMP6, OsZIP10, OsZIP5, and OsZIP9), uniform high level of expression of four genes (OsYSL4, OsNRAMP5, OsNRAMP7 and OsZIP8) and variation in level of expression of rest of the fifteen genes. Out of the total metal homeostasis related candidate genes expressed in flag leaf tissue five genes (OsNAC, OsIRT1, OsZIP4, OsNAS2 and OsYSL2) expressed at uniform high level in all rice genotypes and OsFER2 expressed only in flag leaf tissue. Study of expression pattern of metal related candidate genes in reference to grain Fe/Zn contents of twelve rice genotypes indicated that largely the differential expression of genes at MTS was correlated to difference in grain Zn contents whereas differential expression of metal transporter genes at MGF stage, especially in root tissues, was correlated to the grain Fe contents. Expression of nine genes (OsFER1, OsNRAMP4, OsNRAMP5, OsNRAMP6, OsYSL6, OsYSL12, OsYSL4, OsZIP8, OsZIP10) was found to be correlated to high gain Fe contents, seven genes (OsNAC, OsYSL2, OsYSL9, OsZIP4, OsVIT1, OsNAAT1, OsNRAMP7) to high grain Zn contents whereas expression of two genes (OsFRO2, OsZIP7) was found to be correlated to both high grain Fe and Zn contents. Further functional characterization of these genes will pave way for genomics based improvement of grain Fe and Zn content in rice.