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CRUZ, Aline Bertinatto. Light, ethylene and auxin crosstalk during tomato fruit ripening and carotenogenesis. 2017. 86p. Thesis (Ph.D in Science – Botany) –Bioscience Institute, University of Sao Paulo, Sao Paulo, 2017. 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 β-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. Key-words: Light. Ethylene. Auxins. Fruit ripening. List of abreviations ABA – Abscisic acid ACC – 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID ACO – ACC oxidase ACS – ACC synthase AGPases – ADP-glucose pyrophosphorylases ARF – AUXIN RESPONSE FACTOR Aux/IAA AUXIN/INDOLE-3-ACETIC ACID INDUCIBLE AUX/LAX – AUXIN1/LIKE-AUX1 Bk – Breaker stage Bk1 – 1 days post-breaker Bk12 – 12 days post-breaker Bk3 – 3 days post-breaker Bk6 – 6 days post-breaker CNR – COLORLESS NON-RIPENING COP1 – CONSTITUTIVE PHOTOMORPHOGENESIS 1 CRTISO – CAROTENOID ISOMERASE CRY – cryptochromes CTR – CONSTITUTIVE TRIPLE RESPONSE CUL4 – CULLIN4 CYC-β – LYCOPENE β-CYCLASE DDB1 – DAMAGE DNA BINDING1 DET1 – DETIOLATED1 DMAPP – dimethylallyl diphosphate EIN – ETHYLENE INSENSITIVE ERF – ETHYLENE RESPONSE FACTORS ETR – ETHYLENE RESPONSES flc – Tomato flacca mutant GGPP – geranylgeranyl diphosphate Gr – Tomato Green-ripe mutant HFR1 HYPOCOTYL IN FAR RED 1 HIR – high irradiance responses hp – Tomato high-pigment mutant HY5 – LONG HYPOCOTYL 5 IAA – Indole-3-acetic acid IPP – isopentenyl diphosphate IPyA – indole-3-pyruvic acid JAs Jasmonates LCY-β – LYCOPENE β-CYCLASE LFR – low fluences responses LINs – cell-wall invertases LYC-ε – LYCOPENE ε-CYCLASE MAPKKK – Serine/threonine mitogen-activated protein kinase kinase MEP – methylerythritol MG – Mature green stage NCED – 9-cis-epoxycarotenoid dioxygenase NOR – NON-RIPENING Nr – Tomato Never-ripe mutant PAT – polar auxin transport PDS – PHYTOENE DESATURASE PHY – Phytochromes PIFs PHYTOCHROME INTERACTING FACTORS PIN – PIN-FORMED PSY – PHYTOENE SYNTHASE RIN – RIPENING-INHIBITOR SAM or AdoMet – S-ADENOSYL-METHIONINE SAMS – L-METHIONINE-S-ADENOSYLTRANSFERASE sit – Tomato sitiens mutant SPBP – SQUAMOSA PROMOTER BINDING PROTEIN SUTs – sucrose transporters TAA1 – TRANSLATION OF psaA1 Trp – Tryptophan VLFR – very low fluence responses Z-ISO – ZETA-CAROTENE ISOMERASE ZDS – ZETA-CAROTENE DESATURASE