Recycling of Methylthioadenosine Is Essential for Normal Vascular Development and Reproduction in Arabidopsis    

Abstract

5#-Methylthioadenosine (MTA) is the common by-product of polyamine (PA), nicotianamine (NA), and ethylene biosynthesis in Arabidopsis (Arabidopsis thaliana). The methylthiol moiety of MTA is salvaged by 5#-methylthioadenosine nucleosidase (MTN) in a reaction producing methylthioribose (MTR) and adenine. The MTN double mutant, mtn1-1mtn2-1, retains approximately 14% of the MTN enzyme activity present in the wild type and displays a pleiotropic phenotype that includes altered vasculature and impaired fertility. These abnormal traits were associated with increased MTA levels, altered PA profiles, and reduced NA content. Exogenous feeding of PAs partially recovered fertility, whereas NA supplementation improved fertility and also reversed interveinal chlorosis. The analysis of PA synthase crystal structures containing bound MTA suggests that the corresponding enzyme activities are sensitive to available MTA. Mutant plants that expressed either MTN or human methylthioadenosine phosphorylase (which metabolizes MTA without producing MTR) appeared wild type, proving that the abnormal traits of the mutant are due to MTA accumulation rather than reduced MTR. Based on our results, we propose that the key targets affected by increased MTA content are thermospermine synthase activity and spermidinedependent posttranslational modification of eukaryotic initiation factor 5A.

Phloem-Specific Methionine Recycling Fuels Polyamine Biosynthesis in a Sulfur-Dependent Manner and Promotes Flower and Seed Development

“…S5 and S6). This is in contrast to the results of Waduwara-Jayabahu et al (2012), in which the addition of spermidine had the strongest positive effect. While the mtn1/mtn2 double knockout plants accumulated MTA, which caused feedback inhibition of PA synthases and ultimately lead to thermospermine deficiency with thermospermine-dependent vascular defects, the mti1 and dep1 mutants rather suffered from a lack of spermine and displayed stress-related phenotypes.…”

“…Previous studies showed that the Met Cycle plays an essential role for the biosynthesis of ethylene, NA, and PAs Rzewuski et al, 2007;Waduwara-Jayabahu et al, 2012) and that in Arabidopsis the enzymes MTI1 and DEP1 were able to complement yeast mutants defective in the Met Cycle (Pommerrenig et al, 2011). So far, a characterization of the functional importance of the two enzymes in planta and their involvement in any of the Met Cycledependent pathways was lacking.…”

“…The specific expression of Met Cycle genes in the vasculature is in line with the second essential function of the Met Cycle, which is the degradation of MTA, the by-product of ethylene, nicotianamine, and polyamine biosynthesis. Mutants lacking MTA nucleosidase activity (Bürstenbinder et al, 2010;Waduwara-Jayabahu et al, 2012) also showed hyperproliferation of xylem elements in their vasculature and impaired flower development. These effects have been attributed to elevated MTA levels and inhibited polyamine and nicotianamine (NA) biosynthesis.…”

Targeted Systems Biology Profiling of Tomato Fruit Reveals Coordination of the Yang Cycle and a Distinct Regulation of Ethylene Biosynthesis during Postclimacteric Ripening

“…Perhaps certain Yang cycle metabolites are being translocated between the pericarp tissue and vascular cells for further processing. Recently, it was shown in the Arabidopsis double mtn/ mtk mutant that efficient recycling of MTA by the Yang cycle is essential for vascular tissue development (Waduwara-Jayabahu et al, 2012).…”

Pseudomonas syringae type III effector HopAF1 suppresses plant immunity by targeting methionine recycling to block ethylene induction

“…However, we did use this output as a tool to determine whether our complementation lines contain a functional copy of MTN1. It was previously demonstrated that UBQ promoter-driven MTN1 can complement the mtn1 mtn2 reproductive and morphological defects (74). We generated T1 complementation lines and compared their developmental phenotypes with those of Col-0 and mtn1 mtn2 plants (Fig.…”