Glutamine synthetase of potato (Solanum tuberosum L. cv. Desiree) plants: cell- and organ-specific expression and differential developmental regulation reveal specific roles in nitrogen assimilation and mobilization

Abstract

Potato (Solanum tuberosum L. cv. Dé siré e) glutamine synthetase (GS) (EC 6.3.1.2) gene expression and polypeptide accumulation patterns were analysed in several organs and at several developmental stages. Three GS genes have been identified, one gene encoding plastidic GS (GS2) and two encoding cytosolic GS (GS1) that are differentially expressed in the plant at cellular and organ levels. Specific developmental regulation of different GS genes was also observed. Potato GS seems to be regulated essentially at transcription and/or RNA stability levels. GS2 polypeptides and mRNAs were detected in leaves and their content decreased as leaves senesced. A similar pattern of expression was observed for the GS1 gene Stgs1a. GS1 transcripts and polypeptides were present in all organs analysed and are the only GS detected in nonphotosynthetic tissues and in the later leaf senescing stages. The increase in GS1 during leaf senescence mainly reflected polypeptide and transcript accumulation of the GS1-encoding gene Stgs1b. In situ hybridization results point to a cell-specific expression of GS1 genes within the vascular bundles, Stgs1b being expressed in the xylem and phloem parenchyma cells, and Stgs1a being expressed only in the phloem companion cells. This pattern of spatial distribution and differential developmental regulation of different GS1 genes differs from what has been previously described for genes of other Solanaceae with a high degree of similarity with the ones described here and suggests that distinct GS1 isozymes have specific and possibly distinct roles within the same organ. These new findings highlight the physiological importance of different GS1 isoenzymes in plant nitrogen metabolism.

Protein degradation and nitrogen remobilization during leaf senescence

“…The input for these reactions might come from ~Lcetyl-coenzyme A via the degradation of fatty acids (Baker et ai., 2006), oxaloacetate generated by phosphoenol pyruvate carboxylase, and, further upstream, from glycolysis. The transcriptional upregulation of genes for a number of enzymatic processes in this model has been reported in various senescing plant leaves, such as from Arabidopsis (Buchanan-Wollaston et al, 2003, 2005Lin and Wu, 2004), aspen (Bhalerao et al, 2003), several PopuJus species (A~dersson et al, 2004), potato (Teixeira et al, 2005), cotton (Siren. et al, 2006), and wheat (Kichey et al, 2005;Gregersen and Holm, 2007).…”

“…Overexpression with a specific promoter strongly suggests that NADH-GOGAT is important for the reutilization of transportecl glutamine in developing organs. The increased expression ot: NADH-GOGAT and GS1 have also been identified during leaf senescence in various plant species, including Arabidopsis (Buchanan-Wollaston et al, 2003, 2005Lin and Wu, 2004),various Populus species (Andersson el: al., 2004), aspen (Bhalerao et al, 2003), potato (Solanum tuberosum L.; Teixeira et al, 2005), cotton (Shen et al, 2006), and wheat (Kichey et al, 2005;Gregersen a,nd Holm, 2007). …”

Inoculation of tomato plants (Solanum lycopersicum) with growth-promoting Bacillus subtilis retards whitefly Bemisia tabaci development

“…tabaci interaction in spr2 plants led to the up-regulation of genes involved in nutrient assimilation and mobilization (e.g. glutamine synthetase; Teixeira et al 2005), together with ribosomal and other genes related to protein synthesis (supplementary Table 3). In addition, the BsDN/B.…”

Arginase, glutamine synthetase and glutamate dehydrogenase activities in moist chilled and warm-incubated walnut kernels

“…To be utilized by the growing radicle, cotyledonary-free amino acids initially must be converted into transportable forms (Canovas et al 2007) by appropriate and consecutive activity of amino acid metabolizing enzymes such as arginase (King and Gifford 1997) and GS (Teixeira et al 2005). This conversion might also be affected by cold stimulus in stratification treatment, especially in walnut kernels where protein mobilization commences in non-germinated kernels during release from dormancy (Einali and Sadeghipour 2007).…”