Light, ethylene and auxin crosstalk during tomato fruit ripening and carotenogenesis

• Autor(a) principal: Cruz, Aline Bertinatto
• Data de Publicação: 2017
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: http://www.teses.usp.br/teses/disponiveis/41/41132/tde-05092017-104106/
• topic: Amadurecimento de frutos; Auxinas; Auxins; Ethylene; Etileno; Fruit ripening; Light; Luz

Fruit ripening is a highly coordinated process involving numerous structural, biochemical and physiological changes, many of which are influenced by both endogenous and environmental stimuli. Light signaling and plant hormones such as ethylene and auxins have been identified as important regulators of tomato fruit ripening. However, it is still not fully understood how light and hormonal signaling cascades interact to control the development and physiology of fleshy fruits. By applying a mutant-based approach, this study investigated the potential interconnection among light, auxin and ethylene signaling cascades during tomato fruit ripening and carotenogenesis. Analysis of ethylene and auxin metabolism and signaling in ripening fruits of the light-hyperresponsive high-pigment 2 (hp2) mutant revealed that the loss of HP2 function promotes the transcription of genes encoding key regulators of fruit ripening and increases ethylene signaling along with the increments in carotenoid synthesis and accumulation typically found in this mutant. Compared to the wild type (WT), significant changes in fruit auxin signaling were also observed in the hp2 mutant, including significantly higher activation of the auxin-responsive promoter DR5, severe down-regulation of all AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) genes more closely associated with fruit ripening as well as disturbed transcript abundance of genes encoding AUXIN RESPONSE FACTOR (ARF) transcription factors. Evidence of increased tissue responsivity to ethylene and auxins in hp2 ripening fruits is also provided. Moreover, comparing the auxin and ethylene metabolism and signaling in fruits of the phytochrome chromophore-deficient mutant aurea (au) in relation to the WT genotype provided new insights into the phytochrome-hormonal signaling crosstalk regulating the timing of fruit ripening. Compared to the WT, fruits of the au mutant exhibited a delayed-ripening phenotype, which was associated with the late induction of genes encoding master controllers of ripening, delayed ethylene climacteric production as well as coordinated changes in the expression of auxin signaling-related genes. Besides the temporal changes in hormonal signaling associated with ripening, the deficiency in functional phytochromes also seems to repress the cyclization of lycopene, leading to reduced levels of ?-carotene and lutein in the fruit tissues. Although the exact molecular mechanisms behind the altered hormonal responses in tomato fruits triggered by changes in light signaling remain to be further elucidated, the data obtained in this study provide clear evidence that an intricate crosstalk among light, ethylene and auxin signaling may be involved in controlling tomato fruit ripening and carotenogenesis. Therefore, these findings open up a window of opportunity for further improvement in the regulation of ripening-associated processes through the combined manipulation of hormonal and light signaling-related genes