Arabidopsis is capable of responding to volatile phytostimulants emitted by phytopathogenic microorganisms by triggering plastidic phosphoglucose isomerase independent mechanisms

Abstract

Volatile compounds (VOCs) emitted by phylogenetically diverse microorganisms (including plant pathogens and microbes that do not normally interact mutualistically with plants) promote photosynthesis, growth and accumulation of exceptionally high levels of starch in leaves through cytokinin (CK) regulated processes (Sánchez-López et al. 2016). In VOCs non-treated Arabidopsis plants, plastidic phosphoglucose isomerase (pPGI) plays an important role in photosynthesis and growth likely as a consequence of its involvement in the synthesis of plastidic CKs and/or its participation in the glycolytic and oxidative pentose phosphate pathways. Moreover, this enzyme plays an important role in connecting the Calvin Benson cycle with the starch biosynthetic pathway in leaves. To better elucidate mechanisms involved in the plants´ responses to microbial VOCs, and to investigate the extent to which pPGI is involved in this phenomenon, in this work we characterized pPGI null pgi1-2 Arabidopsis plants cultured in the presence or absence of VOCs emitted by Alternaria alternata. We found that volatile emissions from this fungal phytopathogen promoted growth, photosynthesis and accumulation of plastidic CKs in pgi1-2 plants. Contrary to expectations, mesophyll cells of exposed pgi1-2 leaves accumulated exceptionally high levels of starch. Isobaric labeling based differential proteomic analyses revealed that VOCs 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 are capable of responding to volatile phytostimulants emitted by microorganisms by triggering pPGI independent mechanisms.