Arabidopsis Extra-Large G Proteins (XLGs) in phosphate homeostasis

Sabater Royo, Irene
Ried, Martina (dir.) ; Hothorn, Michael (dir.)

Universidad de Zaragoza, CIEN, 2018
Departamento de Bioquímica y Biología Molecular y Celular,

Graduado en Biotecnología

Resumen: Phosphorus, which is taken up as inorganic phosphate (Pi), is one of the most limiting nutrients for plants. To maintain Pi homeostasis, many proteins (e.g. SPX domain proteins) are involved in signalling pathways to mediate different plant responses. In addition to the canonical heterotrimeric G proteins, the Arabidopsis genome encodes three Gα-like proteins, named Extra-Large G proteins: XLG1, XLG2, and XLG3. This project study the role of XLGs in Pi homeostasis in Arabidopsis thaliana. Analysis of the shoot Pi content showed a decreased accumulation in xlg1-2 and xlg3-2 single mutants, which is more notable in the xlg1-2 xlg3-2 double mutant. Under Pi starvation, the xlg1-2 xlg3-2 double mutant developed longer primary roots compared to wild-type plants, while the single xlg mutants were not significant different. Furthermore, all tested xlg single and double mutants showed a tendency toward increased transcript levels of phosphate starvation induced genes compared to the wild-type. Additionally, yeast two-hybrid assays showed an interaction between SPX proteins and XLG1 and XLG3. AtSPX1, a phosphate-dependent inhibitor of the MYB-type transcription factor Phosphate Starvation Response 1 (PHR1), interacts with both AtXLG1 and AtXLG3. However, AtSPX-MFS1, a vacuolar transporter that mediates phosphate storage, only interacts with AtXLG3. These results suggest that XLGs proteins may play a role in Pi homeostasis together with SPX proteins. To test for brassinosteroid related phenotypes, plants were treated with the brassinosteroid biosynthesis inhibitor brassinazole (BRZ). The xlg3-2 mutant showed a decreased in hypocotyl length compared to wild-type, while the xlg1-2 and spx1-1 mutants did not. The xlg1-2 xlg3-2 double mutant showed the same tendency as the xlg3-2, suggesting that the phenotype is caused by the XLG3 mutation. Taken together, these results suggest that XLGs proteins may be involved in different signaling pathways. Nevertheless, little is known about these signalling proteins, and further studies are needed to define how they work.

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