The role of arginine metabolic pathway during embryogenesis and germination in maritime pine (Pinus pinaster Ait.)

Abstract

Vegetative propagation through somatic embryogenesis is critical in conifer biotechnology towards multivarietal forestry that uses elite varieties to cope with environmental and socio-economic issues. An important and still sub-optimal process during in vitro maturation of somatic embryos (SE) is the biosynthesis and deposition of storage proteins, which are rich in amino acids with high nitrogen (N) content, such as arginine. Mobilization of these N-rich proteins is essential for the germination and production of vigorous somatic seedlings. Somatic embryos accumulate lower levels of N reserves than zygotic embryos (ZE) at a similar stage of development. To understand the molecular basis for this difference, the arginine metabolic pathway has been characterized in maritime pine (Pinus pinaster Ait.). The genes involved in arginine metabolism have been identified and GFP-fusion constructs were used to locate the enzymes in different cellular compartments and clarify their metabolic roles during embryogenesis and germination. Analysis of gene expression during somatic embryo maturation revealed high levels of transcripts for genes involved in the biosynthesis and metabolic utilization of arginine. By contrast, enhanced expression levels were only observed during the last stages of maturation and germination of ZE, consistent with the adequate accumulation and mobilization of protein reserves. These results suggest that arginine metabolism is unbalanced in SE (simultaneous biosynthesis and degradation of arginine) and could explain the lower accumulation of storage proteins observed during the late stages of somatic embryogenesis.

Understanding plant nitrogen nutrition through a laboratory experiment

“…In some circumstances, protein profiles can be markers of the N status of the sample . In the present experience using tomato plants, there are no significant differences, only minor changes, such as the absence of some proteins lower than 37 kDa in the N‐ roots compared with that in N+ roots (Supporting Information Fig.…”

Inorganic Nitrogen Form Determines Nutrient Allocation and Metabolic Responses in Maritime Pine Seedlings

“…L-arginine is synthesized from L-glutamate and is an amino acid with an important role as an N reserve in pine. This amino acid is very abundant in storage proteins and is an important sink for assimilated N surplus [20,36]. Additionally, the metabolite profile in the roots indicates that the availability of C for metabolic processes was reduced in nitrate-fed seedlings ( Figure 6, Table S1).…”

Enzymes Involved in the Biosynthesis of Arginine from Ornithine in Maritime Pine (Pinus pinaster Ait.)

“…However, after the completion of the Arabidopsis genome sequence [ 14 ], it was found that genes encoding most arginine biosynthetic enzymes contain a presequence for chloroplast targeting [ 15 ]. Recent localization studies have confirmed these genomic data and have provided strong evidence showing that the complete pathway is confined to plastids, including the enzymes of ornithine pathway and those involved in the biosynthesis of arginine from ornithine, OTC, ASSY and ASL [ 4 , 16 , 17 ].…”

“…The biosynthesis of arginine can be divided into two pathways: the conversion of glutamate into ornithine and the synthesis of arginine from ornithine through the sequential action of the enzymes ornithine transcarbamylase (OTC), argininosuccinate synthetase (ASSY) and argininosuccinate lyase (ASL) [ 4 , 5 ].…”

“…In fact, somatic embryogenesis in combination with cryopreservation is currently a major biotechnological tool for vegetative propagation of selected maritime pine varieties [ 20 ]. However, previous works have shown a deregulation of the arginine biosynthetic pathway and a lower accumulation of storage proteins during the last steps of somatic embryogenesis [ 4 , 19 ].…”