Abstract
SummaryIn legumes, nitrogen (N) can be stored as ureide allantoin and transported by ureide permease (UPS) from nodules to leaves where it is catabolized to release ammonium and assimilation to amino acids. In non‐leguminous plants especially rice, information on its roles in N metabolism is scarce. Here, we show that OsUPS1 is localized in plasma membranes and are highly expressed in vascular tissues of rice. We further evaluated an activation tagging rice overexpressing OsUPS1 (OsUPS1 OX) under several N regimes. Under normal field conditions, panicles from OsUPS1 OX plants (14 days after flowering (DAF)) showed significant allantoin accumulation. Under hydroponic system at the vegetative stage, plants were exposed to N‐starvation and measured the ammonium in roots after resupplying with ammonium sulphate. OsUPS1 OX plants displayed higher ammonium uptake in roots compared to wild type (WT). When grown under low‐N soil supplemented with different N‐concentrations, OsUPS1 OX exhibited better growth at 50% N showing higher chlorophyll, tiller number and at least 20% increase in shoot and root biomass relative to WT. To further confirm the effects of regulating the expression of OsUPS1, we evaluated whole‐body‐overexpressing plants driven by the GOS2 promoter (OsUPS1 GOS 2) as well as silencing plants (OsUPS1 RNA i). We found significant accumulation of allantoin in leaves, stems and roots of OsUPS1 GOS 2 while in OsUPS1 RNA i allantoin was significantly accumulated in roots. We propose that OsUPS1 is responsible for allantoin partitioning in rice and its overexpression can support plant growth through accumulation of allantoin in sink tissues which can be utilized when N is limiting.
Highlights
In crop production, nitrogen (N) supply and availability greatly influence the growth and yield of plants
We evaluated an activation tagging line where the rice ureide permease 1 gene (OsUPS1) was highly activated due to a T-DNA containing a tetramerized 35S enhance sequence inserted at 1.1 kb upstream of the transcriptional start site of OsUPS1 resulting in allantoin accumulation
The metabolite allantoin is a potential N source in nonleguminous plants which can be utilized under N-limiting conditions, we characterized one of its transporters in rice
Summary
Nitrogen (N) supply and availability greatly influence the growth and yield of plants. To support the increasing demand in crops due to the rapid growth of world population, it is essential for crop researchers and breeders to come up with strategies to sustain production and meet demands. Improvement in crop management and agronomy coupled with conventional breeding and genetic engineering have been the major factors behind increased crop production (Han et al, 2015). For several decades synthetic N in the form of ammonium fertilizers showed to be the most practical way to increase crop production. In global cereal production alone, excessive use of synthetic N showed a dramatic increase from 11.6 Tg in 1961 to 104 Tg in 2006 (Mulvaney et al, 2009). Though high N input can increase yield, plants do not take up these N completely and more than 50% are leached in soils resulting in the contamination of the environment (Gruber and Galloway, 2008)
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