Meta-analysis of grain iron and zinc associated QTLs identified hotspot chromosomal regions and positional candidate genes for breeding biofortified rice.

Biofortification of staple crops with essential micronutrients is the sustainable way to overcome the hidden hunger. A large number of quantitative trait loci (QTL) linked with grain micronutrient contents have been reported in different mapping studies. Identification of consistent QTLs across diverse genetic backgrounds is useful for candidate gene analysis and marker assisted selection of target traits. In this study, an up to date meta-analysis of grain iron and zinc associated QTLs was performed and 48 meta-QTLs (MQTLs) distributed across 12 rice chromosomes were identified. The 95% confidence intervals of identified genomic regions were significantly narrower than the average of their corresponding original QTLs. A total of 9308 genes/transcripts physically located within or near MQTL regions were retrieved and through prioritization of candidate genes (CGs) 663 non-redundant iron and zinc CGs were selected and studied in detailed. Several functionally characterized iron and zinc homoeostasis related genes e.g OsATM3, OsDMAS1, OsFRO2, OsNAS1-3, OsVIT2, OsYSL16, OsZIP3 and OsZIP7 were also included in our MQTL analysis. More than 64% genes were enriched with zinc and iron binding gene ontology terms and were involved in oxidation reduction process, carbohydrate metabolic process, regulation of transcription, trans-membrane transport, response to oxidative stress, cell redox homeostasis and proteolysis etc. In-silico transcriptomic analysis of rice identified 260 CGs which were regulated in response to iron and zinc stresses. We also identified at least 37 genes which were differentially expressed under both stress conditions and majority of these have not been studied in detailed before. Our results strongly indicate that majority of the MQTLs identified in this study are hotspots for grain iron and zinc concentration and are worth of intensive functional studies in near future.