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The study of GRAS transcription factors involvement in fruit ripening and fruit response against Botrytis cinerea
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The GRAS transcription factors (TFs) family is known to participate in processes of plant growth and development. However, their role in fruit development and biotic stresses is unclear. The tomato SlGRAS10 and its grapevine ortholog VviPAT6 were indicated as putative regulators of both climacteric and non-climacteric fruit ripening. Moreover, previous reports with gene expression data suggested a putative role of SlGRA10 in flower fertilization.
The SlGRAS10 and VviPAT6 genes shared high sequence similarity, protein interactions and TFs Binding Sites, however, differences in the cis-regulatory elements and expression pattern indicated a putative ripening specialisation. Some SlGRAS10 mutant lines successfully produced by CRISPR/Cas9 showed a reduced number of seeds suggesting an influence of the gene in seed development. In addition, the reduced carotenoid content at late ripening stage (breaker +10 days) indicated a role of the SlGRAS10 in tomato full ripening regulation, which might influence the expression of key-ripening genes (including MADS-box, carotenoid biosynthesis-related genes and involved in abscisic acid and/or ethylene metabolism). In silico analysis indicated a possible redundant function between SlGRAS10 and the paralog SlGRAS9 in tomato that is being addressed by double mutants already developed and under analysis. Regarding the role of VviPAT6, the results obtained are expected to be supported by an ongoing stable microvine transformation, which will, hopefully, elucidate the role of the gene in non-climacteric fruit ripening.
GRAS genes were also associated with response against the necrotrophic fungus Botrytis cinerea in grape berries. Here, the transcriptomic and metabolomic analysis of green berries infected with B. cinerea (from susceptible and tolerant cultivars) suggested a tolerance centred in pre-existent basal defences, whereas the susceptible cultivar showed an active metabolomic response but insufficient to contain the disease. The basal defence observed was putatively sustained in several signalling pathways, such as protein kinases, Ca2+, TFs (including GRAS), and jasmonates, ethylene, and phenylpropanoids metabolism. On the contrary, the fungal transcriptomic profile suggested an active virulence state on the tolerant cultivar even without visible disease symptoms and less activity in Trincadeira infected berries.
Collectively, our results bring insights regarding the broad spectrum of GRAS activity, from flower fertilization in tomato, to fruit development/ripening, and in biotic stress responses that increase our knowledge about this family and that could be used for crop improvement.
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Botrytis cinerea desenvolvimento do fruto fatores de transcrição GRAS Solanum lycopersicum Vitis vinífera fruit development GRAS transcription factors