Rice F-bZIP transcription factors regulate the zinc deficiency response.

Pedro Humberto Castro,Grmay H Lilay,Diego M Almeida,Ana G L Assunção,Joana G Guedes,Ana Campilho,Hendrik Küpper,Mark G M Aarts,Nelson J M Saibo,Herlander Azevedo

doi:10.1093/jxb/eraa115

Abstract

The F-bZIP transcription factors bZIP19 and bZIP23 are the central regulators of the zinc deficiency response in Arabidopsis, and phylogenetic analysis of F-bZIP homologs across land plants indicates that the regulatory mechanism of the zinc deficiency response may be conserved. Here, we identified the rice F-bZIP homologs and investigated their function. OsbZIP48 and OsbZIP50, but not OsbZIP49, complement the zinc deficiency-hypersensitive Arabidopsis bzip19bzip23 double mutant. Ectopic expression of OsbZIP50 in Arabidopsis significantly increases plant zinc accumulation under control zinc supply, suggesting an altered Zn sensing in OsbZIP50. In addition, we performed a phylogenetic analysis of F-bZIP homologs from representative monocot species that supports the branching of plant F-bZIPs into Group 1 and Group 2. Our results suggest that regulation of the zinc deficiency response in rice is conserved, with OsbZIP48 being a functional homolog of AtbZIP19 and AtbZIP23. A better understanding of the mechanisms behind the Zn deficiency response in rice and other important crops will contribute to develop plant-based strategies to address the problems of Zn deficiency in soils, crops, and cereal-based human diets.

Highlights

Zinc (Zn) is an essential micronutrient for all organisms because of its catalytic and structural roles in many proteins, with Zn-binding proteins estimated at ~10% of eukaryote proteomes (Andreini et al, 2006)
These loci correspond to the rice F group of Arabidopsis basic-leucine zipper proteins (F-bZIPs) members, OsbZIP48 and OsbZIP49, respectively
We identified and functionally characterized F-bZIP members of rice ssp. japonica, namely LOC_Os06g50310, LOC_Os01g58760, and LOC_Os05g41540, addressing their role in the Zn deficiency response.The classification of the bZIP family in Arabidopsis comprises 13 groups (Jakoby et al, 2002; Dröge-Laser et al, 2018) and this classification has been extended to all major lineages of green plants in an evolutionary analysis (Corrêa et al, 2008)

Summary

Introduction

Zinc (Zn) is an essential micronutrient for all organisms because of its catalytic and structural roles in many proteins, with Zn-binding proteins estimated at ~10% of eukaryote proteomes (Andreini et al, 2006). Zn-deficient soils are widespread globally, in large parts of Africa and Asia, affecting yield and nutritional quality of crops (Alloway, 2008). Rice (Oryza sativa L.) is one of the most important food crops worldwide, feeding nearly half of the world’s population, especially. The risk of Zn deficiency is estimated to affect about one-third of the world’s human population, and it can lead to different degrees of growth retardation, immune dysfunction, and cognitive impairment (Prasad, 2009; Wessells and Brown, 2012). Improving Zn use efficiency and Zn accumulation in the edible parts of crops (Zn biofortification), in combination with agronomic strategies, constitute plant-based solutions to tackle these global problems (Cakmak, 2002; White and Broadley, 2009)

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Conclusion