Expression of a bacterial asparagine synthetase gene in oilseed rape (Brassica napus) and its effect on traits related to nitrogen efficiency

Abstract

The investigation and improvement of nitrogen efficiency in oilseed rape (Brassica napus L.) are important issues in rapeseed breeding. The objective of this study was to modify ammonium assimilation in transgenic rapeseed plants through the expression of the Escherichia coli asparagine synthetase (AsnA, E.C. 6.3.1.1) gene under the control of the cauliflower mosaic virus (CaMV) 35S promoter, and to study its influence on amino acid composition in leaves and on seed traits related to nitrogen efficiency. In regenerated transgenic plants, the 37 kDa AsnA protein was detected by Western blot analysis, but was lacking in untransformed control plants of cv. Drakkar. In the transformants, in vitro asparagine synthetase activities ranged from 105 to 185 nmol asparagine mg−1 protein h−1, whereas, in untransformed control plants, only negligible asparagine synthetase activities of up to 5 nmol asparagine mg−1 protein h−1 were found. Despite these significant activities, no changes in the amino acid composition in the leaves or in the phloem of transgenic plants were detectable. In a pot experiment, two transgenic lines expressing the prokaryotic asparagine synthetase clearly performed inferiorly to control plants at limiting nitrogen (N) fertilizer supply. Although the seed N content was increased, the seed yield and the seed N yield were reduced, which was interpreted as an increased nitrate assimilation leading, at limiting N supply, to a reduced seed yield and seed N yield. At high N fertilizer supply, the differences were less pronounced for one transgenic line, whereas the other showed a higher seed N yield and an improved nitrogen harvest index. The results show that the expression of the E. coli asnA gene in oilseed rape could be of advantage at high N supply, but not at limiting N fertilizer supply.

Improving Plant Nitrogen Use Efficiency through Alteration of Amino Acid Transport Processes

“…The amount of N allocated to many seed sinks versus the N taken up by the individual seed might depend not only on the N available to the plant but also on the total number of sinks that develop at the early reproductive phase. Once seeds are established, and especially during the seed-filling phase when N demand is high, competing dynamics might exist between seed number and protein content per seed (Seiffert et al, 2004;Drechsler et al, 2015). In AAP1-OE plants, the increased amounts of phloem amino acids (Fig.…”

“…However, efforts to increase N uptake and NUpE through the manipulation of nitrate and ammonium transporters or associated transcription factors have had only limited success (Fraisier et al, 2000;Yuan et al, 2007;Tsay et al, 2011;Ranathunge et al, 2014;Qu et al, 2015;Araus et al, 2016;Chen et al, 2017). Furthermore, varying outcomes have been reported from the ectopic expression of genes involved in amino acid synthesis and N metabolism (Ameziane et al, 2000;Chichkova et al, 2001;Habash et al, 2001;Yamaya et al, 2002;Seiffert et al, 2004;Good et al, 2007;Shrawat et al, 2008;McAllister et al, 2012;Peña et al, 2017). However, these studies rarely addressed the different components of NUE (i.e.…”

“…Nitrogen utilization efficiency (NUtE) is defined as total seed yield relative to total shoot N content (Moll et al, 1982) and is affected by several physiological factors, including N uptake, metabolism, allocation, and remobilization (Habash et al, 2001;Tsay et al, 2011;Girondé et al, 2015). In addition, regulated transport of N within the plant strongly influences the amount of N allocated to seeds and final seed yields (Rolletschek et al, 2005;Schmidt et al, 2007;Weigelt et al, 2008;Tan et al, 2010;Zhang et al, 2010Zhang et al, , 2015Carter and Tegeder, 2016;Santiago and Tegeder, 2016 Araus et al, 2016;Chen et al, 2017), nitrate allocation (Tsay et al, 2011), N metabolism (Ameziane et al, 2000Chichkova et al, 2001;Habash et al, 2001;Yamaya et al, 2002;Seiffert et al, 2004;Good et al, 2007;Shrawat et al, 2008;Peña et al, 2017), and its regulation (Yanagisawa et al, 2004). While generally successful, these studies often did not address the different components of NUE (i.e.…”

“…Approaches to improve plant NUE have focused mainly on the genetic manipulation of N uptake (Fang et al, 2013; Araus et al, 2016;Chen et al, 2017), nitrate allocation (Tsay et al, 2011), N metabolism (Ameziane et al, 2000;Chichkova et al, 2001;Habash et al, 2001;Yamaya et al, 2002;Seiffert et al, 2004;Good et al, 2007;Shrawat et al, 2008;Peña et al, 2017), and its regulation (Yanagisawa et al, 2004). While generally successful, these studies often did not address the different components of NUE (i.e.…”

Responses of Seed Yield and Quality to Nitrogen Application Levels in Two Oilseed Rape (Brassica napusL.) Varieties Differing in Nitrogen Efficiency

“…Root biomass is probably an important index for evaluation of oilseed rape NAE (Cao et al, 2010). The NUE of oilseed rape was increased by increasing the GOGAT (glutamine oxoglutarate aminotransferase) and GS (glutamine synthetase) activities by a transgenic method (Seiffert et al, 2004).…”