Abstract
A total of 16 BnaGLN1 genes coding for cytosolic glutamine synthetase isoforms (EC 6.3.1.2.) were found in the Brassica napus genome. The total number of BnaGLN1 genes, their phylogenetic relationships, and genetic locations are in agreement with the evolutionary history of Brassica species. Two BnaGLN1.1, two BnaGLN1.2, six BnaGLN1.3, four BnaGLN1.4, and two BnaGLN1.5 genes were found and named according to the standardized nomenclature for the Brassica genus. Gene expression showed conserved responses to nitrogen availability and leaf senescence among the Brassiceae tribe. The BnaGLN1.1 and BnaGLN1.4 families are overexpressed during leaf senescence and in response to nitrogen limitation. The BnaGLN1.2 family is up-regulated under high nitrogen regimes. The members of the BnaGLN1.3 family are not affected by nitrogen availability and are more expressed in stems than in leaves. Expression of the two BnaGLN1.5 genes is almost undetectable in vegetative tissues. Regulations arising from plant interactions with their environment (such as nitrogen resources), final architecture, and therefore sink-source relations in planta, seem to be globally conserved between Arabidopsis and B. napus. Similarities of the coding sequence (CDS) and protein sequences, expression profiles, response to nitrogen availability, and ageing suggest that the roles of the different GLN1 families have been conserved among the Brassiceae tribe. These findings are encouraging the transfer of knowledge from the Arabidopsis model plant to the B. napus crop plant. They are of special interest when considering the role of glutamine synthetase in crop yield and grain quality in maize and wheat.
Highlights
Winter oilseed rape (Brassica napus L.) is the dominant oilseed crop in northern Europe, and nitrogen (N) fertilization is the main operational cost for farmers (50% of the total cost of production)
Sequence assembly and alignments with AtGLN1 mRNA sequences revealed different groups of transcripts that allowed expressed sequence tag (EST) to be grouped and 16 individual contigs that might correspond to different BnaGLN1 genes of B. napus to be extracted (Supplementary Data File S2)
The total number of BnaGLN1 genes, their phylogenetic relationships, and genetic location are in agreement with the evolutionary history of Brassica species
Summary
Winter oilseed rape (Brassica napus L.) is the dominant oilseed crop in northern Europe, and nitrogen (N) fertilization is the main operational cost for farmers (50% of the total cost of production). When compared with other crops, oilseed rape is characterized by low nitrogen use efficiency (NUE) (Rathke et al, 2006). Despite a high N-uptake efficiency (Laine et al, 1993), only half the N originating from fertilizer application is recovered in the seeds (Schjoerring et al, 1995). Oilseed rape is characterized by early leaf shedding and unusual high N loss in senescing falling leaves. Leaf senescence generally corresponds to the mobilization of N reserves from source leaves to sink organs such as seeds (Masclaux-Daubresse et al, 2008). It has been shown that N can be remobilized from senescing leaves to expanding leaves at the vegetative stage (sequential senescence) as well as from senescing leaves to seeds at the reproductive stage (monocarpic senescence) (Malagoli et al, 2005)
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