“…Identification of QTLs or genes that control the concentrations of essential mineral nutrients and toxic trace metals (also known as the ionome) in rice grains can increase the speed and efficiency of the variety improvement process. In the past few decades, many efforts have been made in mapping QTLs regulating the rice grain ionome, and hundreds of genetic loci have been identified for individual elements through bi-parental ( Norton et al, 2010 , 2019 ; Zhang et al, 2014 ; Yu et al, 2015 ; Chen et al, 2019 ; Raza et al, 2019 ; Liu et al, 2020 ; Wang et al, 2020 ) or genome wide association (GWA) mapping approaches ( Norton et al, 2014 ; Huang et al, 2015 ; Yang et al, 2018 ; Tan et al, 2020 ). Among these QTLs, only a small number of causal genes have been identified and functionally characterized, including OsHMA3 , OsCAL1 and OsCd1 for Cd ( Ueno et al, 2010 ; Miyadate et al, 2011 ; Luo et al, 2018 ; Sui et al, 2019 ; Yan et al, 2019 ), OsHMA4 for Cu ( Huang et al, 2016 ), and OsMOT1;1 for molybdenum (Mo) ( Yang et al, 2018 ; Huang et al, 2019 ; Wang et al, 2020 ).…”