Cloning and characterization of nitrate reductase gene in Ulva prolifera (Ulvophyceae, Chlorophyta)

Abstract

Ulva spp. dominates green tides around the world, which are occurring at an accelerated rate. The competitive nitrogen assimilation efficiency in Ulva is suggested to result in ecological success against other seaweeds. However, molecular characterization of genes involved in nitrogen assimilation has not been conducted. Here, we describe the identification of the nitrate reductase (NR) gene from a green seaweed Ulva prolifera, an alga which is responsible for the world's largest green tide in the Yellow Sea. Using rapid amplification of cDNA ends and genome walking, the NR gene from U. prolifera (UpNR) was cloned, which consisted of six introns and seven exons encoding 863 amino acids. According to sequence alignment, the NR in U. prolifera was shown to possess all five essential domains and 21 key invariant residues in plant NRs. The GC content of third codon position of UpNR (82.75%) was as high as those of green microalgae, and the intron number supported a potential loss issue from green microalga to land plant. Real-time quantitative PCR results showed that UpNR transcript level was induced by nitrate and repressed by ammonium, which could not be removed by addition of extra nitrate, indicating that U. prolifera preferred ammonium to nitrate. Urea would not repress NR transcription by itself, while it weakened the induction effect of nitrate, implying it possibly inhibited nitrate uptake rather than nitrate reduction. These results suggest the use of UpNR as a gene-sensor to probe the N assimilation process in green tides caused by Ulva.

Photoprotection by photoinhibitory and PSII-reaction centre quenching controls growth of Ulva rigida (Chlorophyta) and is a pre-requisite for green tide formation

“…At this point, the low NR activity resulting from the pre-incubation was not able to reduce nitrate to nitrite as fast as it entered the cells, which results in the storage of nitrate in the vacuoles (McGlathery et al 1996 ; Lartigue and Sherman 2005 ; Kennison et al 2011 ). Higher nitrate concentrations increased the NR activities through enhanced transcription of the corresponding gene as demonstrated for Ulva prolifera (Guo et al 2017 ). Constant uptake rates during the first eight hours after the transfer suggest that nitrate pools were slowly and continuously filled without reaching capacity within this period of time.…”

Cloning and characterization of nitrate reductase gene in kelp Saccharina japonica (Laminariales, Phaeophyta)

“…4 B). This phenomenon was also observed in green algae, Chlorella ellipsoidea and Ulva prolifera , and explained to be a product inhibition of ammonium which was generated from final reduction of nitrate [ 3 , 44 ]. It should be pointed out that gametophytes of kelp can also live independently, and the expression of SjNR gene in the gametophyte generation is worthy of further investigation in the future.…”

Comparative Genomics of Pseudomonas sp. Strain SI-3 Associated With Macroalga Ulva prolifera, the Causative Species for Green Tide in the Yellow Sea

“…However, the role of DNRA in the bloom of macroalgae has never been considered and studied. Additionally, the interspecific ecological success of U. prolifera has been shown to be partially a result of its higher uptake rate of nitrogen (Luo et al, 2012 ), and is the preferred nitrogen form (Guo et al, 2017 ). Since the nitrate concentration of the Yellow Sea presented increasing trend in the last few decades while the concentration of fluctuated (Li et al, 2015 , 2017 ), we wondered whether coupling of DNRA from associated bacteria with the high nitrogen uptake rate would confer U. prolifera a competitive advantages over other seaweeds in the Yellow Sea against other seaweeds.…”