Ethylene pretreatment drives cytosolic invertase-dependent changes in chloroplast biogenesis, photosynthesis, and metabolism

Improving plant growth and stress tolerance is a significant challenge that affects crop production. Here, we demonstrate that ethylene pretreatment in a critical period during germination accelerates development and leads to larger cotyledons, leaves, and roots with larger cells. Additionally, ethylene pretreatment led to prolonged increases in the number of chloroplasts per cell, larger chloroplasts, and higher CO2 assimilation. All of these responses were eliminated in mutants lacking two cytosolic invertases (CINV1, CINV2). Time-lapse imaging showed that wild-type plants have an initial transient increase in root growth within several hours of ethylene removal and transfer to light. This was followed by a second prolonged increase in growth. The cinv1;cinv2 mutants retained an initial, rapid increase in root growth, but lacked prolonged growth stimulation, indicating that there are two phases to the growth stimulation after ethylene pretreatment, with the second, prolonged phase requiring these invertases. RNA-sequencing and untargeted metabolomics revealed that the cinv1;cinv2 mutants still had responses to ethylene pretreatment, but these responses were attenuated and diverged from wild-type. Thus, these invertases are required for changes in chloroplast number and size, increased photosynthesis, and prolonged stimulation of growth after ethylene pretreatment. Ethylene pretreatment represents a possible new approach to explore as a way to increase plant growth.