S. Panda -  Weizmann Institute of Science, Department of Plant and Environmental Sciences, Rehovot, Israel; Agricultural Research Organization (ARO), Gilat Research Center, Beer Sheva, Israel.

A. Jozwiak - Weizmann Institute of Science, Department of Plant and Environmental Sciences, Rehovot, Israel
P. D. Sonawane - Weizmann Institute of Science, Department of Plant and Environmental Sciences, Rehovot, Israel
J. Szymanski - Leibniz Institute of Plant Genetics and Crop Plant Research, Department of Molecular Genetics, Gatersleben, Germany
A. Vainer - Weizmann Institute of Science, Department of Plant and Environmental Sciences, Rehovot, Israel
Y. Kazachkova - Weizmann Institute of Science, Department of Plant and Environmental Sciences, Rehovot, Israel
V. Dikaya - Ludwig-Maximilians-University of Munich, Department of Biology I, Munich, Germany
A. C. Kamble - Department of Botany, Savitribai Phule Pune University, Pune, India
A. Aharoni - Weizmann Institute of Science, Department of Plant and Environmental Sciences, Rehovot, Israel

Steroidal glycoalkaloids (SGAs) are specialized metabolites primarily produced by Solanaceae. SGAs play a protective role against notorious pests and pathogens. While the core SGA biosynthetic pathway has been investigated to a great extent, this work aims to elucidate the regulation of SGA biosynthesis by jasmonates (JAs) and gibberellins (GAs) to maintain the balance between plant defense and plant development, which remains elusive to date. Here we unravel the key components of JA signaling in light of SGA metabolism, starting from JA biosynthesis and perception. Down-regulation of JAR1 (a biosynthetic gene of bioactive JA) leads to reduction in α-tomatine (the main SGA tomato) levels, while application of methyl jasmonate (MeJA) significantly enhances its production. Additionally, in the jai1 mutant (deficient in the activator of JA signaling - COI) we found irreversible reduction in α-tomatine level, even after MeJA treatment. Transcript analysis shows that this phenotype is due to regulation of SGA biosynthetic genes by JA. Furthermore, transgenic approach reveals JAZ (Jasmonate Zim domain proteins) - mediated negative regulation of SGA biosynthesis. The JAZ-regulated SGA phenotype is due to its physical interaction with MYC1 and MYC2. These two bHLH TFs play a dual role in SGA biosynthesis, by inducing the transcription of SGA biosynthetic genes and JAZ repressor genes. Our work suggested that the jasmonate mediated SGA biosynthesis is post-transcriptionally regulated. We also found a link between JA and GA signaling for regulation of SGA biosynthesis, where GA biosynthesis and signaling negatively regulate SGA production. These results provide the insight into the integration of JA- and GA-signaling which is necessary to regulate SGA biosynthesis in a balanced manner between plant defense and development.