Increasing amino acid supply in pea embryos reveals specific interactions of N and C metabolism, and highlights the importance of mitochondrial metabolism

Abstract

SummaryThe application of nitrogen to legumes regulates seed metabolism and composition. We recently showed that the seed-specific overexpression of amino acid permease VfAAP1 increases amino acid supply, and the levels of N and protein in the seeds. Two consecutive field trials using Pisum sativum AAP1 lines confirmed increases in the levels of N and globulin in seed; however, compensatory changes of sucrose/starch and individual seed weight were also observed. We present a comprehensive analysis of AAP1 seeds using combinatorial transcript and metabolite profiling to monitor the effects of nitrogen supply on seed metabolism. AAP1 seeds have increased amino acids and stimulated gene expression associated with storage protein synthesis, maturation, deposition and vesicle trafficking. Transcript/metabolite changes reveal the channelling of surplus N into the transient storage pools asparagine and arginine, indicating that asparagine synthase is transcriptionally activated by high N levels and/or C limitation. Increased C-acceptor demand for amino acid synthesis, resulting from elevated levels of N in seeds, initiates sucrose mobilization and sucrose-dependent pathways via sucrose synthase, glycolysis and the TCA cycle. The AAP1 seeds display a limitation in C, which leads to the catabolism of arginine, glutamic acid and methionine to putrescine, b-alanine and succinate. Mitochondria are involved in the coordination of C/N metabolism, with branched-chain amino acid catabolism and a c-amino-butyric acid shunt. AAP1 seeds contain higher levels of ABA, which is possibly involved in storage-associated gene expression and the N-dependent stimulation of sucrose mobilization, indicating that a signalling network of C, N and ABA is operating during seed maturation. These results demonstrate that legume seeds have a high capacity to regulate N:C ratios, and highlight the importance of mitochondria in the control of N-C balance and amino acid homeostasis.

A search for factors influencing etioplast–chloroplast transition

“…Thus, it seems that OEP16.1, AroGP1, and CM1 are not involved in etioplast to chloroplast transition in Arabidopsis. Instead the function of OEP16 recently was linked to amino acid transport in planta (51). In this study, the seed-specific overexpression of a plasma membrane-localized amino acid permease in pea led to increased amino acid supply and OEP16 transcripts in embryos.…”

Significance of Light, Sugar, and Amino Acid Supply for Diurnal Gene Regulation in Developing Barley Caryopses

“…Nevertheless, we found five genes for amino acid permeases (AAPs) to be diurnally regulated, out of which three showed a strong correlation to Gln and Glu levels (Supplemental Tables S2 and S7). The diurnal and spatial expression profiles of AAP genes are diverse, and further studies are required to unravel their potential roles in the control of amino acid levels in the developing seeds, as recently described for orthologous AAPs in Arabidopsis and pea (Pisum sativum; Weigelt et al, 2008;Sanders et al, 2009). In addition to amino acids, phloem-derived peptides contribute significantly to the nitrogen status and regulate development in developing seeds (Miranda et al, 2003;Li et al, 2009).…”

Sucrose non-fermenting kinase 1 (SnRK1) coordinates metabolic and hormonal signals during pea cotyledon growth and differentiation

“…Erbi), were grown in 2-L pots in growth chambers under a 16-h light (20°C)/8-h dark (18°C) cycle, or were grown in small glasshouses in a soil bed without further regulation under near-field conditions during the summer season (Weigelt et al, 2008). For measurements of embryos, pods were tagged according to DAP, and embryos were collected in the middle of the light phase and snap-frozen in liquid nitrogen.…”