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Unravelling the role of ASN1 gene in the model legume Lotus japonicus

ABSTRACT: Asparagine constitutes the major form of nitrogen translocated within Lotus japonicus plants. Previous work had indicated that the different genes encoding for asparagine synthetase (ASN genes) show differential patterns of expression in different organs from plants grown under either symbiotic (S) or non-symbiotic (NS) conditions. In this work we use knock out mutants deficient in LjASN1 gene, which is the most highly expressed ASN gene in NS conditions, but much less expressed under S conditions. The analysis of two different lines of LORE 1 Ljasn1 homozygous mutant plants grown in the presence complete nutrient medium (NS) or with Mesorhizobium loti (S) was comparatively examined with respect to the WT. The results obtained indicate that a much higher biomass was produced in Ljasn1 mutants grown under NS conditions compared to the WT, while little difference was observed in the mutant plants compared to the WT under S conditions. The results point out a relationship between the deficiency of the ASN1 gene and growth of L. japonicus plants mainly under NS conditions. Further metabolomic analysis revealed that Ljasn1 mutant plants are quite distinct to WT plants when grown under NS conditions, but not under S conditions, in accordance with previous results. Interestingly, asparagine level was considerably reduced in Ljasn1 mutant plants compared to the WT when plants were grown under NS but not under S conditions, thus confirming the crucial relevance of ASN1 in the asparagine levels found in the plants under NS conditions. The results from whole metabolomics analysis, together with other obtained by RNA seq analysis, indicate that ASN1 deficiency produce important changes in the C/N balance and metabolite allocation of  L. japonicus plants resulting in a higher biomass content.

ORGANISM(S): Lotus japonicus

PROVIDER: GSE283121 | GEO | 2026/02/05

REPOSITORIES: GEO

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Project description:Growth retardation and stress-induced premature plant senescence are accompanied by a severe yield reduction and raise a major agro-economic concern. To improve biomass and yield in agricultural crops under mild stress conditions, the survival must be changed to productivity mode. Our previous successful attempts to delay premature senescence and growth inhibition under abiotic stress conditions by autoregulation of cytokinins (CKs) levels constitute a generic technology toward the development of highly productive plants. Since this technology is based on the induction of CKs synthesis during the age-dependent senescence phase by a senescence-specific promoter (SARK), which is not necessarily regulated by abiotic stress conditions, we developed autoregulating transgenic plants expressing the IPT gene specifically under abiotic stress conditions. The Arabidopsis promoter of the stress-induced metallothionein gene (AtMT) was isolated, fused to the IPT gene and transformed into tobacco plants. The MT::IPT transgenic tobacco plants displayed comparable elevated biomass productivity and maintained growth under drought conditions. To decipher the role and the molecular mechanisms of CKs in reverting the survival transcriptional program to a sustainable plant growth program, we performed gene expression analysis of candidate stress-related genes and found unexpectedly clear downregulation in the CK-overproducing plants. We also investigated kinase activity after applying exogenous CKs to tobacco cell suspensions that were grown in salinity stress. In-gel kinase activity analysis demonstrated CK-dependent deactivation of several stress-related kinases including two of the MAPK components, SIPK and WIPK and the NtOSAK, a member of SnRK2 kinase family, a key component of the ABA signaling cascade. A comprehensive phosphoproteomics analysis of tobacco cells, treated with exogenous CKs under salinity-stress conditions indicated that >50% of the identified phosphoproteins involved in stress responses were dephosphorylated by CKs. We hypothesize that upregulation of CK levels under stress conditions desensitize stress signaling cues through deactivation of kinases that are normally activated under stress conditions. CK-dependent desensitization of environmental stimuli is suggested to attenuate various pathways of the avoidance syndrome including the characteristic growth arrest and the premature senescence while allowing normal growth and metabolic maintenance.

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Unravelling the role of ASN1 gene in the model legume Lotus japonicus

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