Nitric oxide, ethylene and auxin crosstalk mediates greening and plastid development in deetiolating tomato seedlings

• Grant number: 16/09430-6
• Support Opportunities: Regular Research Grants - Publications - Scientific article
• Start date: September 01, 2016
• End date: February 28, 2017
• Field of knowledge: Biological Sciences - Botany - Pant Physiology
• Principal Investigator: Luciano Freschi
• Grantee: Luciano Freschi
• Host Institution: Instituto de Biociências (IB). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

The transition from etiolated to green seedlings involves the conversion of etioplasts into mature chloroplasts via a multifaceted, light-driven process comprising multiple, tightly coordinated signaling networks. Here, we demonstrate that light-induced greening and chloroplast differentiation in tomato (Solanum lycopersicum) seedlings are mediated by an intricate crosstalk among phytochromes, nitric oxide (NO), ethylene and auxins. Genetic and pharmacological evidence indicated that either endogenously produced or exogenously applied NO promotes seedling greening by repressing ethylene biosynthesis and inducing auxin accumulation in tomato cotyledons. Analysis performed in hormonal tomato mutants also demonstrated that NO production itself is negatively and positively regulated by ethylene and auxins, respectively. Representing a major biosynthetic source of NO in tomato cotyledons, nitrate reductase was shown to be under strict control of both phytochrome and hormonal signals. A close NO-phytochrome interaction was revealed by the almost complete recovery of the etiolated phenotype of red light-grown seedlings of the tomato phytochrome-deficient aurea mutant upon NO fumigation. In this mutant, NO supplementation induced cotyledon greening, chloroplast differentiation, and hormonal and gene expression alterations similar to those detected in light-exposed wild-type seedlings. NO negatively impacted transcript accumulation of genes encoding phytochrome, photomorphogenesis-repressor factors and plastid division proteins, revealing that this free radical can mimic transcriptional changes typically triggered by phytochrome-dependent light perception. Therefore, our data indicate that negative and positive regulatory feedback loops orchestrate ethylene-NO and auxin-NO interactions, respectively, during the conversion of colorless etiolated seedlings into green, photosynthetically competent young plants. (AU)