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-MCPgrown 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::b-glucuronidase auxinreporter 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.

The root as a drill

“…In comparison, penetration of wild type roots in Soilrite is almost completely abolished at 2 mL L -1 . 62 In conformity with the observations made with wild type, increasing the dosage of 1-MCP affected also the growth of hypocotyls and roots of the pct1-2 mutant by stimulating root growth and inhibiting hypocotyl elongation (Fig. 1B).…”

“…73,74 To further explore the link between the enhanced PAT in pct1-2 and its resistance to 1-MCP, we treated pct1-2 seedlings with L-buthionine-(S,R)-sulfoximine (BSO), an inhibitor of glutathione biosynthesis that downregulates the expression of several PIN proteins in Arabidopsis such as PIN1, PIN2 and PIN3. 75,76 Similar to the TIBA application, 62 application of BSO together with 1-MCP caused a reduction of DR5 activity both in wild type and pct1-2 roots ( Fig. 2A).…”

“…Since 1-MCP also blocked root penetration in monocots such as rice and wheat, and dicots, such as tobacco and lettuce, this indicated a role of ethylene in regulating root penetration in a wide range of plants. 62 The inhibitory effect of 1-MCP on root penetration was reversed by simultaneous application of ethylene, supporting the role of ethylene signaling in regulating root penetration. The loss of root penetration was also associated with a decline in the expression of the auxinresponse reporter DR5::GUS in the root tips, suggesting an interaction between ethylene and auxin signaling in the regulation of this response.…”

Chromoplast-Specific Carotenoid-Associated Protein Appears to Be Important for Enhanced Accumulation of Carotenoids inhp1Tomato Fruits

“…After 4 h, 1 mL of head-space gas was removed from the boxes and injected into a Porapak T column connected to a gas chromatograph (GC-17A; Shimadzu) as described previously (Santisree et al, 2011). For every sample, ethylene in the head-space gas was measured at least three times using a minimum of three biological replicates at each ripening stage.…”

Light modulates the root tip excision induced lateral root formation in tomato

“…Several studies have indicated that activity of the synthetic consensus auxin reporter, DR5::GUS, closely reflects the auxin induced gene expression in plant tissues. 28,29 The root tips were excised at 4 DAG from DR5::GUS transgenic seedlings and roots were stained for GUS activity 24 h after excision, using a protocol described in Santisree et al 30 In root tip decapitated seedlings, DR5::GUS activity was localized in the pericycle region associated with the primordia of emerging lateral roots (Fig. 1).…”