The formation of fruits is an important step in the life cycle of flowering plants. The process of fruit development is highly regulated and involves the interaction of a complex regulatory network of genes in both space and time. To identify regulatory genes involved in fruit initiation in tomato we analyzed the transcriptomic profile of ovaries from the parthenocarpic PsEND1:barnase transgenic line. This line was generated using the cytotoxic gene barnase targeted to the anthers with the PsEND1 anther-specific promoter from pea. Among the differentially expressed genes we identified SlDOF10 , a gene coding a DNA-binding with one finger (DOF) transcription factor which is activated in unpollinated ovaries of the parthenocarpic plants. SlDOF10 is preferentially expressed in the vasculature of the cotyledons and young leaves and in the root tip. During floral development, expression is visible in the vascular tissue of the sepals, the flower pedicel and in the ovary connecting the placenta with the developing ovules. The induction of the gene was observed in response to exogenous gibberellins and auxins treatments. To evaluate the gene function during reproductive development, we have generated SlDOF10 overexpressing and silencing stable transgenic lines. In particular, down-regulation of SlDOF10 activity led to a decrease in the area occupied by individual vascular bundles in the flower pedicel. Associated with this phenotype we observed induction of parthenocarpic fruit set. In summary, expression and functional analyses revealed a role for SlDOF10 gene in the development of the vascular tissue specifically during reproductive development highlighting the importance of this tissue in the process of fruit set.

SUMMARY The tapetum is a specialized layer of cells within the anther, adjacent to the sporogenous tissue. During its short life, it provides nutrients, molecules and materials to the pollen mother cells and microsporocytes, being essential during callose degradation and pollen wall formation. The interaction between the tapetum and sporogenous cells in Solanum lycopersicum (tomato) plants, despite its importance for breeding purposes, is poorly understood. To investigate this process, gene editing was used to generate loss‐of‐function mutants that showed the complete and specific absence of tapetal cells. These plants were obtained targeting the previously uncharacterized Solyc03g097530 (SlTPD1) gene, essential for tapetum specification in tomato plants. In the absence of tapetum, sporogenous cells developed and callose deposition was observed. However, sporocytes failed to undergo the process of meiosis and finally degenerated, leading to male sterility. Transcriptomic analysis conducted in mutant anthers lacking tapetum revealed the downregulation of a set of genes related to redox homeostasis. Indeed, mutant anthers showed a reduction in the accumulation of reactive oxygen species (ROS) at early stages and altered activity of ROS‐scavenging enzymes. The results obtained highlight the importance of the tapetal tissue in maintaining redox homeostasis during male gametogenesis in tomato plants.

The tapetum is a specialized layer of cells within the anther adjacent to the sporogenic tissue. During its short life, it provides nutrients, molecules and materials to the pollen mother cells and microsporocytes being essential during callose degradation and pollen wall formation. However, the acquisition of tapetal cell identity in tomato plants is a process still poorly understood. We report here the identification and characterization of SlTPD1 (Solanum lycopersicum TPD1), a gene specifically required for pollen development in tomato plants. Gene editing was used to generate loss-of-function Sltpd1 mutants that showed absence of tapetal tissue. In these plants, sporogenous cells developed but failed to complete meiosis resulting in complete male sterility. Transcriptomic analysis conducted in wild-type and mutant anthers at an early stage revealed the down regulation of a set of genes related to redox homeostasis. Indeed, Sltpd1 anthers showed a reduction of reactive oxygen species (ROS) accumulation at early stages and altered activity of ROS scavenging enzymes. The obtained results highlight the importance of ROS homeostasis in the interaction between the tapetum and the sporogenous tissue in tomato plants.One sentence summaryThe small protein SlTPD1 is required for tapetum formation in tomato, highlighting the role of this tissue in the regulation of redox homeostasis during male gametogenesis.