AUTHOR=Moreno-Moyano Laura T. , Bonneau Julien P. , Sánchez-Palacios José T. , Tohme Joseph , Johnson Alexander A. T. 

TITLE=Association of Increased Grain Iron and Zinc Concentrations with Agro-morphological Traits of Biofortified Rice

JOURNAL=Frontiers in Plant Science

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.01463

DOI=10.3389/fpls.2016.01463

ISSN=1664-462X

ABSTRACT=<p>Biofortification of rice (<italic>Oryza sativa</italic> L.) 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 (<italic>OsNAS</italic>) 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 (BC<sub>2</sub>F<sub>2</sub>) transgenic progeny carrying <italic>OsNAS1</italic> or <italic>OsNAS2</italic> overexpression constructs under <italic>indica/japonica</italic> and <italic>japonica/japonica</italic> genetic backgrounds. Thirteen agro-morphological traits were evaluated in BC<sub>2</sub>F<sub>2</sub> transgenic 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 BC<sub>2</sub>F<sub>2</sub> transgenic 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<sup>-1</sup> and 40 μg Zn g<sup>-1</sup> in BC<sub>2</sub>F<sub>2</sub><italic>indica/japonica</italic> progeny, and 36 μg Fe g<sup>-1</sup> and 56 μg Zn g<sup>1</sup> in BC<sub>2</sub>F<sub>2</sub><italic>japonica/japonica</italic> progeny, 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 the <italic>indica/japonica</italic> and <italic>japonica/japonica</italic> background, respectively. We subsequently produced polished grain from high-yield BC<sub>2</sub>F<sub>2</sub> transgenic progeny carrying either the <italic>OsNAS1</italic> or <italic>OsNAS2</italic> overexpression constructs. The <italic>OsNAS2</italic> overexpressing progeny had higher percentages of Fe and Zn in polished rice grain compared to the <italic>OsNAS1</italic> overexpressing 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 by <italic>OsNAS2</italic> overexpression and monitoring for Zn overaccumulation in the grain.</p>