Volatile compounds emitted by diverse phytopathogenic microorganisms promote plant growth and flowering through cytokinin action

Sánchez-López, Ángela María et al.It is known that volatile emissions from some beneficial rhizosphere microorganisms promote plant growth. Here we show that volatile compounds (VCs) emitted by phylogenetically diverse rhizosphere and non-rhizhosphere bacteria and fungi (including plant pathogens and microbes that do not normally interact mutualistically with plants) promote growth and flowering of various plant species, including crops. In Arabidopsis plants exposed to VCs emitted by the phytopathogen Alternaria alternata, changes included enhancement of photosynthesis and accumulation of high levels of cytokinins (CKs) and sugars. Evidence obtained using transgenic Arabidopsis plants with altered CK status show that CKs play essential roles in this phenomenon, because growth and flowering responses to the VCs were reduced in mutants with CK-deficiency (35S:AtCKX1) or low receptor sensitivity (ahk2/3). Further, we demonstrate that the plant responses to fungal VCs are light-dependent. Transcriptomic analyses of Arabidopsis leaves exposed to A. alternata VCs revealed changes in the expression of light- and CK-responsive genes involved in photosynthesis, growth and flowering. Notably, many genes differentially expressed in plants treated with fungal VCs were also differentially expressed in plants exposed to VCs emitted by the plant growth promoting rhizobacterium Bacillus subtilis GB03, suggesting that plants react to microbial VCs through highly conserved regulatory mechanisms.This work was partially supported by the Comisión Interministerial de Ciencia y Tecnología and Fondo Europeo de Desarrollo Regional (Spain) (grant numbers BIO2010-18239 and BIO2013- 49125-C2-1-P), the Government of Navarra (grant number IIM010491.RI1), the I-Link0939 project from the Ministerio de Economía y Competitividad, the Ministry of Education, Youth and Sports of the Czech Republic (Grant L01204 from the National Program of Sustainability) and Palacky University institutional support. AM S-L and P G-G gratefully acknowledge predoctoral fellowships from the Spanish Ministry of Science and Innovation. M B and G A acknowledge post-doctoral fellowships awarded by the Public University of Navarra.Peer reviewe

Characterization of multiple SPS knockout mutants reveals redundant functions of the four Arabidopsis sucrose phosphate synthase isoforms in plant viability, and strongly indicates that enhanced respiration and accelerated starch turnover can alleviate the blockage of sucrose biosynthesis

We characterized multiple knock-out mutants of the four Arabidopsis sucrose phosphate synthase (SPSA1, SPSA2, SPSB and SPSC) isoforms. Despite their reduced SPS activity, spsa1/spsa2, spsa1/spsb, spsa2/spsb, spsa2/spsc, spsb/spsc, spsa1/spsa2/spsb and spsa2/spsb/spsc mutants displayed wild type (WT) vegetative and reproductive morphology, and showed WT photosynthetic capacity and respiration. In contrast, growth of rosettes, flowers and siliques of the spsa1/spsc and spsa1/spsa2/spsc mutants was reduced compared with WT plants. Furthermore, these plants displayed a high dark respiration phenotype. spsa1/spsb/spsc and spsa1/spsa2/spsb/spsc seeds poorly germinated and produced aberrant and sterile plants. Leaves of all viable sps mutants, except spsa1/spsc and spsa1/spsa2/spsc, accumulated WT levels of nonstructural carbohydrates. spsa1/spsc leaves possessed high levels of metabolic intermediates and activities of enzymes of the glycolytic and tricarboxylic acid cycle pathways, and accumulated high levels of metabolic intermediates of the nocturnal starch-to-sucrose conversion process, even under continuous light conditions. Results presented in this work show that SPS is essential for plant viability, reveal redundant functions of the four SPS isoforms in processes that are important for plant growth and nonstructural carbohydrate metabolism, and strongly indicate that accelerated starch turnover and enhanced respiration can alleviate the blockage of sucrose biosynthesis in spsa1/spsc leaves.This work was partially supported by the Comisión Interministerial de Ciencia y Tecnología and Fondo Europeo de Desarrollo Regional (Spain) [grant numbers BIO2010-18239, BIO2013-49125-C2-1-P, BIO2008-02292 and BIO2011-28847-C02-02]. A.M.S-L. acknowledges a predoctoral fellowship from the Spanish Ministry of Science and Innovation. M.B. acknowledges a post-doctoral fellowship from the Public University of Navarra.Peer Reviewe

Arabidopsis responds to Alternaria alternata volatiles by triggering plastid phosphoglucose isomerase-independent mechanisms

Sánchez-López, Ángela María et al.Volatile compounds (VCs) emitted by phylogenetically diverse microorganisms (including plant pathogens and microbes that do not normally interact mutualistically with plants) promote photosynthesis, growth, and the accumulation of high levels of starch in leaves through cytokinin (CK)-regulated processes. In Arabidopsis (Arabidopsis thaliana) plants not exposed to VCs, plastidic phosphoglucose isomerase (pPGI) acts as an important determinant of photosynthesis and growth, likely as a consequence of its involvement in the synthesis of plastidic CKs in roots. Moreover, this enzyme plays an important role in connecting the Calvin-Benson cycle with the starch biosynthetic pathway in leaves. To elucidate the mechanisms involved in the responses of plants to microbial VCs and to investigate the extent of pPGI involvement, we characterized pPGI-null pgi1-2 Arabidopsis plants cultured in the presence or absence of VCs emitted by Alternaria alternata. We found that volatile emissions from this fungal phytopathogen promote growth, photosynthesis, and the accumulation of plastidic CKs in pgi1-2 leaves. Notably, the mesophyll cells of pgi1-2 leaves accumulated exceptionally high levels of starch following VC exposure. Proteomic analyses revealed that VCs promote global changes in the expression of proteins involved in photosynthesis, starch metabolism, and growth that can account for the observed responses in pgi1-2 plants. The overall data show that Arabidopsis plants can respond to VCs emitted by phytopathogenic microorganisms by triggering pPGI-independent mechanisms.This work was supported by the Comisión Interministerial de Ciencia y Tecnología and Fondo Europeo de Desarrollo Regional, Spain (grant nos. BIO2010–18239 and BIO2013–49125–C2–1–P), by the Government of Navarra (grant no. IIM010491.RI1), by the I-Link0939 project from the Ministerio de Economía y Competitividad, by the Ministry of Education, Youth, and Sports of the Czech Republic (grant no. LO1204 from the National Program of Sustainability), by Palacky University institutional support, by predoctoral fellowships from the Spanish Ministry of Science and Innovation (to A.M.S.-L. and P.G.-G.), and by postdoctoral fellowships from the Public University of Navarra (to M.B. and G.A.).Peer Reviewe

Volatile compounds emitted by Gram-negative and Gram-positive bacteria and fungi promote growth and starch accumulation through cytokinin regulated processes

Póster presentado en el Fresh & glycoprotein symposium, celebrado en Japón en septiembre de 2015.It is known that volatile emissions from some beneficial rhizobacteria promote growth in plants. Here we show that volatile compounds emitted by the plant pathogen Alternaria alternata promote growth and the accumulation of exceptionally high levels of starch in leaves. Analyses of the volatile exometabolome of this species allowed us to identify several volatile compounds that promote plant growth and drastic metabolic changes. In Arabidopsis,this phenomenon (initially designated as MIVOISAP, for Microbial VOIatiles Induced Starch Accumulation Process) was accompanied by enhanced photosynthetic capacity, likely as a consequence of increased levels of plastidic type of cytokinins (CK). The magnitude of the phenomenon was low in mutants impaired in photoreceptors, CK receptors, plastidial NADP-thioredoxin reductase C(NTRC) and plastidic phosphoglucose isomerase. The overall data showed that (a) production of volatiles promoting plant growth is not restricted to beneficial rhizobacterial species, and (b) Arabidopsis MIVOISAP involves complex photocontrolled processes where in photoreceptors, NTRC－mediated changes in redox status of plastidial target proteins, CK production and signaling play important roles.Peer Reviewe

Volatile compounds emitted by the plant pathogen Alternaria alternata promote photosynthesis, growth and accumulation of high levels of starch in Arabidopsis through pPGI dependent and independent cytokinin biosynthetic processes

Póster presentado en el XXI Reunión de la Sociedad Española de Fisiología Vegetal y el XIV Congreso Hispano-Luso Fisiología Vegetal, celebrado en Toledo del 14 al 17 de junio de 2015.Peer Reviewe

Volatile compounds emitted by the plant pathogen Alternaria alternata enhance photosynthesis and promote growth of Arabidopsis by increasing cytokinin production

Póster presentado en el Fresh & glycoprotein symposium, celebrado en Japón en septiembre de 2015.Peer Reviewe

Volatile compounds emitted by a wide range of rhizosphere and non-rhizosphere microorganisms promote growth through cytokinin regulated processes

Trabajo presentado en la International Conference "Plant Biotechnology: Green for Good III", celebrada en Olomouc (República Checa) del 15 al 18 de junio de 2015.Peer Reviewe

Soil application of volatile compounds emitted by the plant pathogen Alternaria alternata enhance yield of pepper plants cultured under greenhouse conditions

Póster presentado en la International Conference "Plant Biotechnology: Green for Good III", celebrada en Olomouc (República Checa) del 15 al 18 de junio de 2015.Peer Reviewe

Arabidopsis plants lacking plastid phosphoglucose isomerase respond to microbial volatiles through GLUCOSE-6-P/PHOSPHATE TRANSLOCATOR2 action

Resumen del trabajo presentado en la XXIV Reunión de la Sociedad Española de Biología de Plantas - XVII Congreso Hispano-Luso de Biología de Plantas, celebrado online del 7 al 9 de julio de 2021Recent studies have shown that PGI1 is an important determinant of photosynthesis, growth and starch production, likely as a consequence of its involvement in the synthesis of plastidial isoprenoid compounds such as hormones and photosynthetic pigments (Bahaji et al. 2015; Bahaji et al. 2018). We have shown that volatile compounds (VCs) emitted by microbes promote growth, photosynthesis, and accumulation of cytokinins (CK) and starch (Sánchez-Lopez et al. 2016a). This response was PGI1-independent, as fungal VCs exposed PGI1 null pgi1-2 plants grew faster and accumulated exceedingly higher levels of starch and CKs than plants not exposed to VCs (Sánchez-López et al. 2016b). The most up-regulated gene in leaves of fungal VCs exposed plants was At1g61800, encoding the plastidial GPT2 glucose-6-phosphate (G6P)/phosphate translocator. Whether the response of pgi1-2 to fungal VCs could be due to the GPT2-mediated transport of cytosolic G6P into the chloroplast was investigated by characterizing pgi1-2/gpt2-2 PGI1- and GPT2-null double mutants cultured in the presence or absence of VCs emitted by the fungal phytopathogen Alternaria alternata. We found that photosynthesis, active CKs content, growth and leaf starch content in pgi1-2/gpt2-2 plants exposed to fungal VCs were lower than in VCs exposed WT, gpt2-2 and pgi1-2 plants. Proteomic analyses revealed that fungal VCs strongly up-regulate the expression of proteins involved in photosynthesis in WT, gpt2-2 and pgi1-2 plants, but in much lower extent in pgi1-2/gpt2-2 plants. The overall data show that the combined action of PGI1 and GTP2 is an important determinant of the plant´s response to microbial VCs. The possible involvement of these functions in the production of growth- and foliar metabolism-regulating isoprenoid hormones in heterotrophic organs is discussed.This work was supported by the Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (Spain) (grants BIO2016-78747-P and PID2019-104685GB-100) and the Ministry of Education, Youth and Sport of the Czech Republic and ERDF project “Plants as a tool for sustainable global development” (No. CZ.02.1.01/0.0/0.0/16_019/0000827).Peer reviewe

Plastidic phosphoglucose isomerase is an important determinant of starch accumulation in mesophyll cells, growth, photosynthetic capacity, and biosynthesis of plastidic cytokinins in Arabidopsis

Póster presentado en el XXI Reunión de la Sociedad Española de Fisiología Vegetal y el XIV Congreso Hispano-Luso Fisiología Vegetal, celebrado en Toledo del 14 al 17 de junio de 2015.Peer Reviewe