title: Tomato root penetration in soil requires a coaction between ethylene and auxin signaling.
abstract: During seed germination, emerging roots display positive gravitropism and penetrate into the soil for nutrition and anchorage. Tomato (Solanum lycopersicum) seeds germinated in the presence of 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action, failed to insert roots into Soilrite and grew in the air, forming loops. Time-lapse video imaging showed that 1-MCP-grown root tips retained positive gravitropism and made contact with the surface of Soilrite but failed to penetrate into the Soilrite. Time-course studies revealed that the effect of 1-MCP was most prominent when seed imbibition and germination were carried out in the continual presence of 1-MCP. Conversely, 1-MCP was ineffective when applied postgermination after penetration of roots in the Soilrite. Furthermore, treatment with 1-MCP caused a reduction in DR5::β-glucuronidase auxin-reporter activity and modified the expression of SlIAA3 and SlIAA9 transcripts, indicating interference with auxin signaling. The reduced ethylene perception mutant, Never-ripe, displayed decreased ability for root penetration, and the enhanced polar auxin transport mutant, polycotyledon, showed a nearly normal root penetration in the presence of 1-MCP, which could be reversed by application of auxin transport inhibitors. Our results indicate that during tomato seed germination, a coaction between ethylene and auxin is required for root penetration into the soil.
authors.affiliation: School of Life Sciences, University of Hyderabad, Hyderabad 500046, India.
authors.forename: Parankusam
authors.initials: P
authors.lastname: Santisree
authors.forename: Sapana
authors.initials: S
authors.lastname: Nongmaithem
authors.forename: Himabindu
authors.initials: H
authors.lastname: Vasuki
authors.forename: Yellamaraju
authors.initials: Y
authors.lastname: Sreelakshmi
authors.forename: Maria G
authors.initials: MG
authors.lastname: Ivanchenko
authors.forename: Rameshwar
authors.initials: R
authors.lastname: Sharma
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D003521:Cyclopropanes / Q000494:pharmacology; D005030:Ethylenes / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D018522:Gravitropism / Q000187:drug effects; D007210:Indoleacetic Acids / Q000378:metabolism*; D018551:Solanum lycopersicum / Q000187:drug effects / Q000254:growth & development*; D040542:Mechanotransduction, Cellular / Q000187:drug effects / Q000235:genetics; D018519:Meristem / Q000187:drug effects / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development*; D036226:Seedlings / Q000187:drug effects / Q000254:growth & development; D015398:Signal Transduction / Q000187:drug effects; D012987:Soil
chemical_list: D003521:Cyclopropanes; D005030:Ethylenes; D007210:Indoleacetic Acids; D012987:Soil; C036216:ethylene; C412563:1-methylcyclopropene