Comparative Expression Analysis of Metal Homeostasis-Related Genes in Rice Genotypes Differing in Grain Micronutrient Levels

To understand the role of metal homeostasis-related genes in rice, micronutrient levels of different tissue types were analysed at mid grain-filling stage followed by the expression analysis of candidate genes in these tissues. Subsequently, the association between the gene expression pattern and micronutrient level in tissues as well as mature grains was analysed. Out of 11 candidate genes used for gene expression analysis utilizing bulked cDNA based RT-PCR, 8 genes showed high level of expression in flag leaf and second leaf tissues. Four genes showed poor level of expression in immature grains and low to negligible expression in stem tissues. Further, six candidate genes were selected based on differential response of cDNA bulk analysis for the expression studies of individual rice genotypes, including four high-zinc rice genotypes, namely R-RHZ-LI-25, IR92970-111-1-2, R-RHZ-SM- 3, R-RHZ-SM-4 which showed higher level of expression for genes OsVIT1, OsFER1, OsYSL2 and OsYSL9. Whereas low or negligible level gene expression in stem tissue of five genes, except OsFER1 shows that rice stem tissue could be involved in the uptake of micronutrients. The thorough characterization of genes in this study provides deeper insight into the tightly regulated mechanism of metal homeostasis with respect to different tissue types and understanding of source-sink relationship of mineral acquisition and remobilization.