title: Association of Increased Grain Iron and Zinc Concentrations with Agro-morphological Traits of Biofortified Rice.
abstract: Biofortification of rice (Oryza sativaL.) with micronutrients is widely recognized as a sustainable strategy to alleviate human iron (Fe) and zinc (Zn) deficiencies in developing countries where rice is the staple food. Constitutive overexpression of the rice nicotianamine synthase (OsNAS) genes has been successfully implemented to increase Fe and Zn concentrations in unpolished and polished rice grain. Intensive research is now needed to couple this high-micronutrient trait with high grain yields. We investigated associations of increased grain Fe and Zn concentrations with agro-morphological traits of backcross twice second filial (BC2F2) transgenic progeny carryingOsNAS1orOsNAS2overexpression constructs underindica/japonicaandjaponica/japonicagenetic backgrounds. Thirteen agro-morphological traits were evaluated in BC2F2transgenic progeny grown under hydroponic conditions. Concentrations of eight mineral nutrients (Fe, Zn, copper, manganese, calcium, magnesium, potassium, and phosphorus) in roots, stems/sheaths, non-flag leaves, flag leaves, panicles, and grain were also determined. A distance-based linear model (DistLM) was utilized to extract plant tissue nutrient predictors accounting for the largest variation in agro-morphological traits differing between transgenic and non-transgenic progeny. Overall, the BC2F2transgenic progeny contained up to 148% higher Fe and 336% higher Zn concentrations in unpolished grain compared to non-transgenic progeny. However, unpolished grain concentrations surpassing 23 μg Fe g-1and 40 μg Zn g-1in BC2F2indica/japonicaprogeny, and 36 μg Fe g-1and 56 μg Zn g1in BC2F2japonica/japonicaprogeny, were associated with significant reductions in grain yield. DistLM analyses identified grain-Zn and panicle-magnesium as the primary nutrient predictors associated with grain yield reductions in theindica/japonicaandjaponica/japonicabackground, respectively. We subsequently produced polished grain from high-yield BC2F2transgenic progeny carrying either theOsNAS1orOsNAS2overexpression constructs. TheOsNAS2overexpressing progeny had higher percentages of Fe and Zn in polished rice grain compared to theOsNAS1overexpressing progeny. Results from this study demonstrate that genetic background has a major effect on the development of Fe and Zn biofortified rice. Moreover, our study shows that high-yielding rice lines with Fe and Zn biofortified polished grain can be developed byOsNAS2overexpression and monitoring for Zn overaccumulation in the grain.
authors.affiliation: School of BioSciences, The University of Melbourne, Melbourne VIC, Australia.
authors.forename: Laura T
authors.initials: LT
authors.lastname: Moreno-Moyano
authors.affiliation: School of BioSciences, The University of Melbourne, Melbourne VIC, Australia.
authors.forename: Julien P
authors.initials: JP
authors.lastname: Bonneau
authors.affiliation: School of BioSciences, The University of Melbourne, Melbourne VIC, Australia.
authors.forename: José T
authors.initials: JT
authors.lastname: Sánchez-Palacios
authors.affiliation: International Center for Tropical Agriculture Cali, Colombia.
authors.forename: Joseph
authors.initials: J
authors.lastname: Tohme
authors.affiliation: School of BioSciences, The University of Melbourne, Melbourne VIC, Australia.
authors.forename: Alexander A T
authors.initials: AA
authors.lastname: Johnson
keywords: OsNAS2; biofortification; magnesium; nicotianamine synthase; overaccumulation; panicle; yield