Abstract
Background: Nicotianamine (NA) serves as not only the major chelator for iron transport but also the intermediate for synthesizing mugineic acid family phytosiderophores (MAs) which are secreted by graminaceous plants for Fe uptake. Therefore, the production and secretion of MAs are key steps for maintaining iron homeostasis in plants. Nicotianamine aminotransferase (NAAT), 2’-deoxymugineic acid synthase (DMAS), MAs efflux transporter (TOM), and efflux transporter of NA (ENA) were identified to be involved in these processes in rice and barley, whereas little systematic study has been performed in maize (Zea mays.L). Results: Here, we identified five ZmNAAT, nine ZmDMAS, eleven ZmTOM, and two ZmENA genes in maize by genome mining. RNA-sequencing (RNA-seq) and quantitative real-time PCR (qRT-PCR) analysis revealed that the expression of these genes exhibited diverse tissue specificity and different responses to environmental iron conditions. Moreover, the expression patterns were related to their evolution relationships. In particular, the ZmNAAT family can be classified into two subgroups, with one group showed inhibited expression in root under iron excess status and another subclass were repressed in shoot under both iron deficiency and excess. Likewise, the expression of ZmDMAS1 was stimulated under iron deficiency, while the remaining genes fell into two sub-clades with different expression patterns. Significant up-regulation of ZmTOM1, ZmTOM3 and ZmENA1 were observed under iron starvation, while ZmTOM2 was induced under both iron-excess and deficiency. These results reflect changing demands for the synthesis and secretion of NA/MAs to balance iron homeostasis under fluctuating conditions. All the examined ZmNAAT and ZmDMAS proteins localized in cytoplasm, while plasma and tonoplast membrane, endomembrane, and vesicle localization were observed for ZmTOM and ZmENA proteins. These results indicate that ZmTOM and ZmENA proteins may contribute to not only intercellular export but also intracellular sequestration of NA and MAs to facilitate iron homeostasis. Conclusions: Our results suggest that different gene expression profiles and subcellular localization of ZmNAAT, ZmDMAS, ZmTOM, and ZmENA members may enable dedicate regulation of NA and phytosiderophores (PS) metabolism, shedding light on the understanding of iron-homeostasis in maize. Additionally, we also provided candidate genes for breeding iron-rich maize varieties.
CLEC-2 contributes to hemostasis independently of classical hemITAM signaling in mice