Role of the Phosphorylated Pathway of Serine Biosynthesis in plant response to biotic stress under climate change conditions
- Autores: Andrea Alcántara Enguidanos
- Directores de la Tesis: Roque Luis Ros Palau (codir. tes.), Sara Rosa Téllez (codir. tes.)
- Lectura: En la Universitat de València ( España ) en 2026
- Idioma: inglés
- Número de páginas: 252
- Tribunal Calificador de la Tesis: Juan Segura García del Río (presid.), Edurne Baroja Fernández (secret.), Laise Rosado De Souza (voc.)
- Programa de doctorado: Programa de Doctorado en Biomedicina y Biotecnología por la Universitat de València (Estudi General)
- Menciones:
- Internacional
- Calificación: Sobresaliente Cum Laude
- Materias:
- Enlaces
- Resumen
Greenhouse gas emissions, par0cularly the increase in atmospheric carbon dioxide (CO2), are intensifying global climate change, driving higher temperatures and more frequent extreme weather events. This scenario presents a significant challenge for agriculture, as plants must adapt to these changes through mechanisms such as metabolic reprogramming. In this way, serine has emerged as a key metabolite in plant metabolism, playing a central role in linking carbon (C), nitrogen (N), and sulfur (S) metabolism, and it could be an important determinant in plant responses to stress.
The elevated CO₂ concentra0on (eCO₂) generates an unbalance in plant metabolism caused by the drop of the photorespira0on flux and, therefore, the reduc0on of serine and glycine pools synthe0zed via the Glycolate Pathway of Serine Biosynthesis (GPSB). In response to this environmental change, plants upregulate the genes of the Phosphorylated Pathway of Serine Biosynthesis (PPSB) to maintain the necessary amino acid supply. This shiL is crucial not only for sustaining primary metabolism but also for suppor0ng defense-related processes, as serine is a precursor of glucosinolates, bioac0ve nitrogen-sulfur-containing compounds involved in plant immunity. This thesis aims to elucidate the interconnec0on of GSPB and PPSB, how their ac0vi0es modulate N and S metabolism, as well as the contribu0on of PPSB to plant responses to bio0c stress, par0cularly in the context of climate change. This work is framed within the Sustainable Development Goals (SDGs), contribu0ng to the development of sustainable crop improvement strategies.
In the first part of the study, Arabidopsis thaliana deficient mutants in the PPSB and the serine- hydroxymethyltransferase 1 (SHMT1), a central enzyme of the GPSB, were studied, including double mutants. PPSB-deficient plants displayed severe primary root growth inhibi0on, while the disrup0on of SHMT1 in the PPSB-deficient mutants background par0ally restored root development. GraLing experiments and metabolic profiling confirmed that SHMT1 influences root metabolism through metabolic fluxes origina0ng from photosynthe0c 0ssues. Addi0onally, RNA-sequencing (RNA-seq) analysis revealed that PPSB-deficient plants exhibited transcrip0onal profiles indica0ve of N and S starva0on, which were absent in the double mutants. The findings highlight a novel metabolic integra0on point: the serine-glycine-one-carbon network. This network influences systemic metabolic balance across plant organs by modula0ng N and S assimila0on pathways.
The second chapter aimed to iden0fy candidate genes involved in nutrient-deficiency responses in PPSB-deficient plants. Transcriptomic analyses revealed upregula0on of PYD4, a gene encoding an enzyme involved in pyrimidine catabolism and iden0fied as a poten0al alanine:glyoxylate aminotransferase. Func0onal analyses of PYD4 loss-of-func0on mutants, par0cularly in a PPSB-deficient background, revealed a surprising phenotype: enhanced shoot biomass and root length, sugges0ng that PYD4 modulates glycine availability, probably through aspartate and amino acids-derived metabolism, which in turn may compensate for impaired serine biosynthesis under PPSB deficiency. These results emphasize the significance of the PYD4 enzyme in restoring the glycine-serine balance and maintaining overall N and S metabolic homeostasis. Metabolomic data supported these findings, reinforcing the central role of PYD4 in modula0ng amino acid balance and improving nutrient-deficiency phenotypes.
The third chapter inves0gated the role of PPSB in the synthesis of defense-related metabolites, focusing on glucosinolates produc0on under climate change condi0ons. Compara0ve analyses showed that PPSB-deficient plants accumulated higher levels of glucosinolates than wild-type (WT) under ambient CO₂ concentra0on but failed to do so under eCO₂. This suggests that PPSB- derived serine is cri0cal for maintaining glucosinolate synthesis in changing environments.
To further inves0gate the connec0on between primary and specialized metabolism, transgenic Arabidopsis lines were generated to overexpress PPSB genes (OexPGDH1 and OexPGDH2) in combina0on with the transcrip0on factors MYB34/ATR1 and MYB51, both involved in the regula0on of indolic glucosinolate biosynthesis. Phenotypic analysis revealed contras0ng roles: the atr1D mutant, which acts as an overexpression line due to the more steady-state levels of ATR1 transcript, exhibited reduced growth, while MYB51 overexpressing lines (OexMYB51) showed enhanced root development. Double overexpressing lines displayed intermediate phenotypes, reflec0ng the metabolic trade-off between growth and defense.
Upon infec0on with Botry6s cinerea, metabolomic profiling revealed increased glycine, nitrogen- related amino acids, and soluble sugars in atr1D and double overexpressing lines, par0cularly under eCO₂, indica0ng enhanced serine-to-glycine flux and ac0va0on of defense metabolism.
This translated into elevated indolic glucosinolate levels, sugges0ng a stronger metabolic defense response mediated by ATR1 in conjunc0on with PPSB-derived serine. In contrast, OexMYB51 lines showed a dis0nct profile: no significant changes in serine, glycine, or N-compound levels were observed compared to WT plants, under either CO₂ condi0on or pathogen stress. Interes0ngly, OexPGDH2 lines accumulated the highest serine levels, followed by the double overexpressing lines. However, serine content in double overexpressing lines was notably lower than in single OexPGDH2, especially under eCO₂, sugges0ng that MYB51 may par0ally suppress serine accumula0on. Nonetheless, this serine pool supported greater glucosinolate produc0on, par0cularly in double overexpressing under stress, highligh0ng the key role of PPSB ac0vity in linking amino acid metabolism with plant defenses under climate change condi0ons. The integra0on of these findings shed light on the precise contribu0on of the PPSB to plant immunity and resilience. The evidence gathered so far posi0ons PPSB as a cri0cal regulatory node that links primary metabolism (serine-glycine-N/S homeostasis) with plant defense mechanisms and growth responses under climate stress.
In conclusion, this thesis provides gene0c and biochemical evidence highligh0ng the integra0ve role of the serine biosynthesis network, par0cularly the PPSB, in coordina0ng nutri0onal status, metabolic homeostasis, and plant defense under climate change condi0ons. The results not only advance our fundamental understanding of plant metabolic plas0city but also contribute to the development of sustainable strategies for crop improvement aligned with the SDGs of the 2030 Agenda.
