Alleviation of Nitrogen and Sulfur Deficiency and Enhancement of Photosynthesis in Arabidopsis thaliana by Overexpression of Uroporphyrinogen III Methyltransferase (UPM1). AtUPM1 [At5g40850] was used to produce both sense and antisense plants of Arabidopsis thaliana in order to modulate siroheme biosynthesis.  Our results clearly demonstrate that upregulation of siroheme biosynthesis leads to increased nitrogen and sulfur assimilation, and this imparts tolerance to nitrogen and sulfur deficiency in Arabidopsis thaliana plants.
Arabidopsis
AtUPM1 [At5g40850] was used to produce both sense and antisense plants of Arabidopsis thaliana in order to modulate siroheme biosynthesis.  In our experiments, overexpression of AtUPM1 signaled higher NiR (NII) and SiR gene and gene product expression.  We suggest that elevated NiR, NR, and SiR expression must have contributed to the increased synthesis of S containing amino acids in AtUPM1overexpressors, observed in our studies. 
AtUPM1
Increased NII expression was found to regulate and enhance the transcript and protein abundance of nitrate reductase (NR). 
nitrate reductase (NR)
Siroheme, an iron-containing tetrapyrrole, is the prosthetic group of nitrite reductase (NiR) and sulfite reductase (SiR); it is synthesized from uroporphyrinogen III, an intermediate of chlorophyll biosynthesis, and is required for nitrogen (N) and sulfur (S) assimilation. 
sulfite reductase (SiR)
Siroheme, an iron-containing tetrapyrrole, is the prosthetic group of nitrite reductase (NiR) and sulfite reductase (SiR); it is synthesized from uroporphyrinogen III, an intermediate of chlorophyll biosynthesis, and is required for nitrogen (N) and sulfur (S) assimilation. 
nitrite reductase (NiR)