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. 2022 Sep 15;63(9):1298-1308.
doi: 10.1093/pcp/pcac103.

A Role for Allantoate Amidohydrolase (AtAAH) in the Germination of Arabidopsis thaliana Seeds

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A Role for Allantoate Amidohydrolase (AtAAH) in the Germination of Arabidopsis thaliana Seeds

Farzaneh Yazdanpanah et al. Plant Cell Physiol. .

Abstract

Seed dormancy is a very complex trait controlled by interactions between genetic and environmental factors. Nitrate is inversely correlated with seed dormancy in Arabidopsis. This is explained by the fact that seed dry storage (after-ripening) reduces the need for nitrogen for germination. When nitrate is absorbed by plants, it is first reduced to nitrite and then to ammonium for incorporation into amino acids, nucleic acids and chlorophyll. Previously, we showed that ALLANTOATE AMIDOHYDROLASE (AtAAH) transcripts are up-regulated in imbibed dormant seeds compared with after-ripened seeds. AAH is an enzyme in the uric acid catabolic pathway which catalyzes the hydrolysis of allantoate to yield CO2, NH3 and S-ureidoglycine. This pathway is the final stage of purine catabolism, and functions in plants and some bacteria to provide nitrogen, particularly when other nitrogen sources are depleted. Ataah mutant seeds are more dormant and accumulate high levels of allantoate, allantoin and urea, whereas energy-related metabolites and several amino acids are lower upon seed imbibition in comparison with Columbia-0. AtAAH expression could be detected during the early stages of seed development, with a transient increase around 8 d after pollination. AtAAH expression is the highest in mature pollen. The application of exogenous potassium nitrate can partly complement the higher dormancy phenotype of the Ataah mutant seeds, whereas other nitrogen sources cannot. Our results indicate that potassium nitrate does not specifically overcome the alleviated dormancy levels in Ataah mutant seeds, but promotes germination in general. Possible pathways by which AtAAH affects seed germination are discussed.

Keywords: Arabidopsis thaliana; Ammonia; Block of germination; Nitrogen; Purine pathway; Seed dormancy.

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Figures

Fig. 1
Fig. 1
The S-allantoin degradation pathway and the effect of a defective AtAAH enzyme on Arabidopsis seed phenotypes. (A) Schematic presentation of S-allantoin degradation in plants. Conversions in the pathway and the enzymes responsible are indicated. (B) Open silique of the Ataah mutant in comparison with Columbia-0 (Col-0). The mutant contains several defective seeds indicated by the arrows. (C) Seed dormancy levels expressed as days of seed dry storage to reach 50% of germination (DSDS50) of Ataah, and of Col-0 and two independent Ataah complementation lines. (D) Seed performance of after-ripened seeds (germination after artificial aging and germination in stress conditions including: salt 130 mM; mannitol (−1 MPa) and ABA (0.15 µM)). Shown are averages of four biological replicates and their SE. Significant differences between Ataah and Col-0 are indicated (*P < 0.05 and **P < 0.01).
Fig. 2
Fig. 2
Expression pattern of ALLANTONATE AMIDOHYDROLASE (AtAAH) during plant development. (A) Mean relative expression levels of AtAAH measured by RT–qPCR in tissues of the Columbia accession leaf (L), flower (F), seedling (SE), root (R) and stem (ST) in siliques 3, 8 13 and18 d after pollination (DAP), in dormant dry (D) and 6 h imbibed seeds (6hD), and across the germination time course in after-ripened dry (ARD) seeds and 6, 12, 24, 35, 48 and 73 h after imbibition. Expression values are normalized by the expression of two reference genes that are stably expressed in dry seeds: At4g12590 and At4g34270. (B) AtAAH expression patterns measured by qbasePLUS software in dormant and non-dormant (after-ripened) dry Cvi seeds and the micropylar and chalazal endosperm (ME) and radicle and hypocotyl (RAD) at 3, 7, 12 and 24 h after imbibition. Asterisks indicate significant differences between dormant and non-dormant in AtAAH expression (***P < 0.001; **P < 0.01; *P < 0.05).
Fig. 3
Fig. 3
Effect of different nitrate regimes during seed maturation on seed performance. Seed performance of both Ataah and Col-0 is presented. (A) Dormancy level (DSDS50), (B) germination in salt (130 mM NaCl), (C) germination in mannitol (−1 MPa), (D) germination in ABA (0.15 μM) of seeds matured on plants exposed to different nitrate levels (N0, N5 and N20). Shown are averages of four biological replicates and their SE. Significant differences between Ataah and Col-0 are indicated by *** (P < 0.001) and different letters (Student t-tests; P < 0.05).
Fig. 4
Fig. 4
Effect of applying nitrogen-containing compounds during seed imbibition. Germination percentage of Ataah and Col-0 after applying (A) KNO3 (10 mM), (B) NH4NO3 (10 mM) and (C) NH4Cl (10 mM) during seed imbibition. Means of maximum germination percentage from four replicates are presented. Significant differences between Ataah and the control Col-0 are indicated (*P < 0.05, **P < 0.01 and ***P < 0.001). The experiments presented in (A–C) were all performed at the same time; the KNO3, NH4NO3 and NH4Cl treatments are compared with the same water control. (D) Germination percentage of Col-0, Ataah and two independent Ataah complementation lines in the presence of the nitrate reductase inhibitor tungsten (Na2WO4), with and without addition of 10 mM KNO3. The experiment was performed 28 d after seed harvest when the Ataah seeds had not yet after-ripened. Means of maximum germination percentage from four replicates are presented. Differences are indicated by different letters (Student t-tests; P < 0.05).
Fig. 5
Fig. 5
Relative expression of genes in the purine pathway related to allantoate degradation: AtAAH (A), AtALN (B), URE (C), UAH (D) and UGLYAH (E). Plant material consisted of seeds of Col and the ataah mutant matured on plants exposed to different nitrate levels. Means of relative expression level (reference genes At3g25800 and At4g34270) from four replicates are presented. Error bars represent the SEs, and different letters indicate statistically significant differences (Student t-tests; P < 0.05).
Fig. 6
Fig. 6
(A) Metabolic profiles of seeds of Col-0 and the Ataah mutant. Allantoate, allantoate and ureidoglycolate concentrations in Col-0, Ataah and two independent Ataah complementation lines. (B) Ammonium content of Col-0, Ataah and two independent Ataah complementation lines. (C) Metabolite levels (mg DW−1) in 24 h imbibed dormant seeds of Col-0 and the Ataah mutant. Asterisks indicate significant differences relative to the respective wild type (***P < 0.001; **P < 0.01).

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References

    1. Alamillo J.M., Díaz-Leal J.L., SÁnchez-Moran M.V., Pineda M., (2010) Molecular analysis of ureide accumulation under drought stress in Phaseolus vulgaris L. Plant Cell Environ. 33: 1828–1837. - PubMed
    1. Alboresi A., Gestin C., Leydecker M.T., Bedu M., Meyer C. and Truong H.N. (2005) Nitrate, a signal relieving seed dormancy in Arabidopsis. Plant Cell Environ. 28: 500–512. - PubMed
    1. Ali-Rachedi S., Bouinot D., Wagner M.H., Bonnet M., Sotta B., Grappin P., et al. (2004) Changes in endogenous abscisic acid levels during dormancy release and maintenance of mature seeds: studies with the Cape Verde Islands ecotype, the dormant model of Arabidopsis thaliana. Planta 219: 479–488. - PubMed
    1. Alonso J.M., Stepanova A.N., Leisse T.J., Kim C.J., Chen H., Shinn P., et al. (2003) Genome-wide insertional mutagenesis of Arabidopsis thaliana. Science 301: 653–657. - PubMed
    1. Arc E., Sechet J., Corbineau F., Rajjou L. and Marion-Poll A. (2013) ABA crosstalk with ethylene and nitric oxide in seed dormancy and germination. Front. Plant Sci. 4: 63. - PMC - PubMed