Transition to ripening in tomato requires hormone-controlled genetic reprogramming initiated in gel tissue.

Ripening is the last stage of the developmental program in fleshy fruits. During this phase, fruits become edible and acquire their unique sensory qualities and post-harvest potential. Although our knowledge of the mechanisms that regulate fruit ripening has improved considerably over the past decades, the processes that trigger the transition to ripening remain poorly deciphered. While transcriptomic profiling of tomato (Solanum lycopersicum L.) fruit ripening to date has mainly focused on the changes occurring in pericarp tissues between the Mature Green and Breaker stages, our study addresses the changes between the Early Mature Green and Late Mature Green stages in the gel and pericarp separately. The data showed that the shift from an inability to initiate ripening to the capacity to undergo full ripening requires extensive transcriptomic reprogramming that takes place first in the locular tissues before extending to the pericarp. Genome-wide transcriptomic profiling revealed the wide diversity of transcription factor (TF) families engaged in the global reprogramming of gene expression and identified those specifically regulated at the Mature Green stage in the gel but not in the pericarp, thereby providing potential targets toward deciphering the initial factors and events that trigger the transition to ripening. The study also uncovered an extensive reformed homeostasis for most plant hormones, highlighting the multihormonal control of ripening initiation. Our data unveil the antagonistic roles of ethylene and auxin during the onset of ripening and show that auxin treatment delays fruit ripening via impairing the expression of genes required for System-2 autocatalytic ethylene production that is essential for climacteric ripening. This study unveils the detailed features of the transcriptomic reprogramming associated with the transition to ripening of tomato fruit and shows that the first changes occur in the locular gel before extending to pericarp and that a reformed auxin homeostasis is essential for the ripening to proceed.

Overexpression of bHLH95, a basic helix-loop-helix transcription factor family member, impacts trichome formation via regulating gibberellin biosynthesis in tomato.

Trichomes are epidermal protuberances on aerial parts of plants known to play an important role in biotic and abiotic stresses. To date, our knowledge of the regulation of trichome formation in crop species is very limited. Through phenotyping of the Solanum pennellii×S. lycopersicum (cv. M82) introgression population, we identified the SlbHLH95 transcription factor as a negative regulator of trichome formation in tomato. In line with this negative role, SlbHLH95 displayed a very low expression in stems where trichomes are present at high density. Overexpression of SlbHLH95 resulted in a dramatically reduced trichome density in stems and a significant down-regulation of a set of trichome-related genes. In addition to the lower trichome density, overexpressing lines also showed pleiotropic alterations affecting both vegetative and reproductive development. While most of these phenotypes were reminiscent of gibberellin (GA)-deficient phenotypes, expression studies showed that two GA biosynthesis genes, SlGA20ox2 and SlKS5, are significantly down-regulated in SlbHLH95-OE plants. Moreover, in line with a decrease in active GA content, the glabrous and dwarf phenotypes were rescued by exogenous GA treatment. In addition, yeast one-hybrid and transactivation assays revealed that SlbHLH95 represses the expression of SlGA20ox2 and SlKS5 via direct binding to their promoters. Taken together, our study established a link between SlbHLH95, GA, and trichome formation, and uncovered the role of this gene in modulating GA biosynthesis in tomato.

Trichome regulator SlMIXTA-like directly manipulates primary metabolism in tomato fruit.

Trichomes are storage compartments for specialized metabolites in many plant species. In trichome, plant primary metabolism is significantly changed, providing substrates for downstream secondary metabolism. However, little is known of how plants coordinate trichome formation and primary metabolism regulation. In this report, tomato (Solanum lycopersicum) trichome regulator SlMIXTA-like is indicated as a metabolic regulation gene by mGWAS analysis. Overexpression of SlMIXTA-like in tomato fruit enhances trichome formation. In addition, SlMIXTA-like can directly bind to the promoter region of gene encoding 3-deoxy-7-phosphoheptulonate synthase (SlDAHPS) to activate its expression. Induction of SlDAHPS expression enhances shikimate pathway activities and provides substrates for downstream secondary metabolism. Our data provide direct evidence that trichome regulator can directly manipulate primary metabolism, in which way plants can coordinate metabolic regulation and the formation of storage compartments for specialized metabolites. The newly identified SlMIXTA-like can be used for future metabolic engineering.