Nitrogen deficiency and senescence in Arabidopsis and oilseed rape: Transcriptome response and the role of nitrate transporters
Zusammenfassung der Projektergebnisse
The overall aim of this project was to advance the understanding of N remobilization and allocation mechanisms in oilseed rape and its close relative Arabidopsis thaliana during nitrogen starvation and developmental senescence. (1) We investigated the role of the Arabidopsis NRT1.5 transporter during N deficiency. (2) We performed a transcriptome analysis of Brassica napus leaves at different stages of N deficiency-induced and developmental senescence. (3) We developed early gene expression markers for a low N supply status. (1) NRT1.5 has been reported to be expressed in roots and to function as a bi-directional NO3- transporter. We found that NRT1.5 is strongly upregulated in senescing leaves and thus hypothesized that the transporter might be involved in N remobilization from senescing leaves and that NRT1.5 overexpression could improve NUE of the plants. We investigated the molecular and physiological responses of Arabidopsis wild type (Col-0) and nrt1.5 T-DNA insertion lines grown on normal and low N fertilized soil. nrt1.5 mutant plants developed an early senescence phenotype under low N supply, however, NO3- and total N contents in the rosette were not reduced but even slightly enhanced compared to wild type plants. In contrast, the potassium concentration was reduced to 30% in young leaves, suggesting that early senescence is caused by K deficiency in nrt1.5 shoots. In roots, K levels were not reduced, indicating that the presence of NRT1.5 in roots is a prerequisite for proper root-toshoot translocation of K+ under low NO3-supply. Furthermore, we found evidence for functional interaction of NRT1.5 with the K transporter SKOR. SKOR mediates K+ root-to-shoot translocation under high NO3- and low K+ availability, while NRT1.5 is important for K+ translocation under low NO3-availability irrespective of the K+ supply. Our results suggest that NRT1.5 and SKOR contribute synergistically to the ability of a plant to adapt to varying NO3- and K+ concentrations in the soil. However, the increased expression of NRT1.5 in senescing leaves does not improve N remobilization. (2) For genome wide transcriptome analyses in oilseed rape leaves, we developed a dedicated B. napus microarray which was used in the three FOR948 projects TP1, TP4 and TP6. We investigated developmental and N deficiency-induced transcription changes in leaves of B. napus cv. Mozart plants which were supplied by TP6. In an older leaf (whorl #4), under low N supply senescence-related transcriptome reorganization began approximately one week earlier and in total more genes were regulated than under optimal N supply. In particular under low N supply the upregulation of BnSAG12, ubiquitin-dependent and -independent protein degradation and nucleotide degradation pathway genes as well as the downregulation of chlorophyll biosynthesis, photosynthesis, pectin esterases and cell wall biosynthesis genes was accelerated. In contrast, in younger sink leaves (whorl #8) of plants grown under N limitation up- or downregulation of senescence-associated genes was delayed compared to plants grown under normal N supply. We hypothesize that delayed senescence initiation under N deficiency in upper leaves contributes to a better N remobilization efficiency. (3) The senescence markers 'SAG12 induction' and 'SPAD value decrease' indicate N deficiency of oilseed rape plants at a progressed state. In cooperation with TP9, TP5 and TP2 we identified 13 markers that consistently detected N deficiency earlier than SAG12 and SPAD in eight B. napus cultivars, grown in climate chambers, greenhouse and on the open field. These genes constitute a candidate gene set for a universal B. napus early N deficiency biomarker kit.
Projektbezogene Publikationen (Auswahl)
- (2015) Nitrate-dependent control of shoot K homeostasis by the Nitrate Transporter1/Peptide Transporter Family member NPF7.3/NRT1.5 and the Stelar K+ Outward Rectifier SKOR in Arabidopsis. Plant Physiol. 169, 2832-2847
Drechsler, N., Zheng, Y., Bohner, A., Nobmann, B., von Wirén, N., Kunze, R., Rausch, C.
(Siehe online unter https://doi.org/10.1104/pp.15.01152) - (2015) Transcriptomic analysis of nitrogen starvationand cultivar-specific leaf senescence in winter oilseed rape (Brassica napus L.). Plant Sci. 233, 174-185
Koeslin-Findeklee, F., Safavi Rizi, V., Becker, M.A., Parra-Londono, S., Arif, M., Balazadeh, S., Mueller-Roeber, B., Kunze, R., Horst, W.J.
(Siehe online unter https://doi.org/10.1016/j.plantsci.2014.11.018)
