Arabidopsis polyamine biosynthesis: absence of ornithine decarboxylase and the mechanism of arginine decarboxylase activity

Abstract

SummaryUnlike other eukaryotes, which can synthesize polyamines only from ornithine, plants possess an additional pathway from arginine. Occasionally non-enzymatic decarboxylation of ornithine could be detected in Arabidopsis extracts; however, we could not detect ornithine decarboxylase (ODC; EC 4. 1.1.17) enzymatic activity or any activity inhibitory to the ODC assay. There are no intact or degraded ODC sequences in the Arabidopsis genome and no ODC expressed sequence tags. Arabidopsis is therefore the only plant and one of only two eukaryotic organisms (the other being the protozoan Trypanosoma cruzi) that have been demonstrated to lack ODC activity. As ODC is a key enzyme in polyamine biosynthesis, Arabidopsis is reliant on the additional arginine decarboxylase (ADC; EC 4.1.1.9) pathway, found only in plants and some bacteria, to synthesize putrescine. By using site-directed mutants of the Arabidopsis ADC1 and heterologous expression in yeast, we show that ADC, like ODC, is a head-to-tail homodimer with two active sites acting in trans across the interface of the dimer. Amino acids K136 and C524 of Arabidopsis ADC1 are essential for activity and participate in separate active sites. Maximal activity of Arabidopsis ADC1 in yeast requires the presence of general protease genes, and it is likely that dimer formation precedes proteolytic processing of the ADC pre-protein monomer.

Arginase-Negative Mutants of Arabidopsis Exhibit Increased Nitric Oxide Signaling in Root Development

“…By our model, diminished arginase activity in argah1-1 or argah2-1 will make more Arg available for NOS activity or for the synthesis of the polyamine, spermine. Arabidopsis lacks ODC (Hanfrey et al, 2001), so the only Arg-to-spermine route is via ADC (Fig. 5).…”

“…Two further enzyme-catalyzed reactions convert the ADC reaction product, agmatine, to putrescine (Illingworth et al, 2003), a precursor of spermidine, and then to spermine. Arabidopsis lacks an ODC (Hanfrey et al, 2001); hence, the ODC-catalyzed conversion of Orn to spermine, via putrescine and spermidine, is shown as blocked.…”

“…Spermine is produced from putrescine, which can be produced from Arg by either of two routes: (1) via arginase to Orn and then to putrescine via Orn decarboxylase (ODC), or (2) via Arg decarboxylase (ADC) to agmatine and then, via N-carbamoylputrescine, to putrescine (Illingworth et al, 2003). Arabidopsis was reported to lack ODC, having only two differentially expressed forms of ADC (Hanfrey et al, 2001;Hummel et al, 2004). If there is no ODC in Arabidopsis, arginase action could diminish the availability of Arg to ADC and the subsequent formation of spermine via pathway 2.…”

The Role of Polyamines in Plant Disease Resistance

“…The first is the single-step conversion of ornithine to Put, which is catalyzed by ornithine decarboxylase (ODC); however, some plant species, including members of the genus Arabidopsis, have lost this pathway (Hanfrey et al, 2001). The other pathway comprises three sequential reactions in which arginine is converted to agmatine by arginine decarboxylase (ADC), agmatine is converted to N-carbamoylputrescine by agmatine iminohydrolase, and N-carbamoylputrescine is converted to Put by N-carbamoylputrescine amidohydrolase.…”

Role of Polyamines in Efficiency of Norway Spruce (Hurst Ecotype) Somatic Embryogenesis

“…Decrease or arrest of internal PA production inhibits a row of cellular functions, e. g. cell growth. Therefore, in the case of PAs deficiency, plant cells are equipped with a high efficient system for transfer and functional utilization of PA molecules from external sources (Cohen, 1998, Hanfrey et al, 2001, Kusano et al, 2008.…”