Characterization of Arabidopsis thaliana proteins containing an EXS domain on Pi transport and homeostasis


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PhD thesis: a PhD thesis.
Characterization of Arabidopsis thaliana proteins containing an EXS domain on Pi transport and homeostasis
Hsieh Yi-Fang
Poirier Yves
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Université de Lausanne, Faculté de biologie et médecine
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Phosphorus (P) is an important macronutrient for normal growth in plants. PHOl (PHOSPHATE 1), involved in phosphate (Pi) export from roots to shoots, contains at the N­ terminus a hydrophilic SPX (SYG1/Pho81/XPR1) domain required for binding inositol pyrophosphate, a hydrophobic EXS (ERDI/XPRI/SYG1) domain at the C-terminus and four transmembrane domains (4TM) in between. The EXS domain of PHO1 is essential for the protein localization to the Golgi/TGN (trans-Golgi network) and the truncated form without the SPX domain (4TM-EXS) harbored the Pi export function but could not complement the pho1 mutant. To better understand the function of the EXS domain, we focused on two other proteins in Arabidopsis, ERDlA and ERDlB, which contain the EXS domain, yet, without an associated SPX domain. Using T-DNA mutants in these genes, we found that Joss of ERDlA resulted in stunted growth and Jack of mature pollen, while the erd1b mutant did not have a significant phenotype. Bath ERD1A and ERD1B localized to the Golgi and were broadly expressed in various tissues. Although the expression level of ERD1A was much higher than ERD1B, overexpression of ERDlB could complement the erd1a mutant phenotypes suggesting that these two proteins have the same function. No erd1a erd1b could be generated, indicating that the absence of both genes is lethal to plants. Previous studies regarding the homolog of ERD1A/B in yeast, ScERD1, suggested that ScERDl is involved in Pi transport in Golgi, an important organelle involved glycosylation and protein trafficking. Ectopic expression of ERDlA and ERDlB in the yeast erd1a mutant could partially complement the mutant Pi export phenotype. Thus, we hypothesized ERDlA and ERDlB were also engaged in Golgi Pi transport in plants. More Pi export was detected in erd1a seedlings compared to Col-0 and the tobacco leaves expressing ERDlA also exported more Pi. However, the root and shoot Pi content of the erd1a mutant did not show significant difference compared to Col-0. Furthermore, the cell wall monosaccharide composition was altered in erd1a, implying that the flux of nucleotide sugars towards cell wall synthesis in Golgi was affected. Additionally, elongation of bath etiolated hypocotyl and pollen tube, which require rapid cell wall synthesis, were strongly impaired in erd1a. Overall, our findings reveal that ERDlA plays an important role in plant cell growth and development and is associated with Pi homeostasis and glycosylation in Golgi.
Create date
03/02/2022 13:06
Last modification date
04/02/2022 7:35
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