**6. Advances in the understanding of molecular mechanisms underlying seed/fruit set and development**

Underlying molecular mechanisms of seed set and development in angiosperms is becoming clear rapidly with the advancements of various omics studies such as genomics, transcriptomics and proteomics etc. and genetic transformation techniques. These mechanisms are generally conserved across all the angiosperms and may also be operated in vegetables. Various studies have been conducted in vegetables such as tomato (and cucumber to explore the underlying molecular mechanism of seed set and fruit set) [38]. In 2016, isolated and characterised two allelic mutants, twisted seed1-1 (tws1-1) and tws1-2 of a single copy gene (TWS1). This gene encodes a small protein of 81 amino acids which regulates embryonic development and accumulation of storage compounds in the seed [39].

This gene is specifically conserved among angiosperms and can be cloned from vegetables to explore its function in seed development in vegetables. The importance of AN3-MINI3 gene cascade in seed embryo development. Their regulatory model provided a deep insight into the seed mass regulation, which may be further explored to increase seed yields of vegetables [40]. Role of mitochondrial reactive oxygen species homeostasis in gametophyte and seed development has also been highlighted in angiosperms. It was reported that the effect of the mutation in *AtHEMN1* gene which encodes for coproporphyrinogen III oxidase. They showed adverse effects of *Athemn1* mutant alleles on gametophytic and seed development. Adverse effects included the development of nonviable pollen and embryo sacs with unfused polar nuclei, defects in endosperm development due to abnormal differentiation of the central cell and arresting of embryo development at the globular stage [41].

To ensure successful sexual plant reproduction, fruit set or transformation of flowers to fruits is very critical. Role of hormones (i.e. auxin and gibberellins) in controlling fruit set after pollination and fertilisation have been well understood. It was shown that the role of microRNA-based (microRNA159/GAMYB1 and −2 pathway) regulation ovary development and fruit set in tomato. They initiated fruit set by modulating auxin and gibberellin responses using SlGAMYBs. On the other hand, proteins such as TIR1-like proteins have also been shown to have essential roles in auxin-mediated fruit development processes. Two TIR1-like genes have been identified in cucumber and designated as CsTIR1 and CsAFB2 [42]. Xu et al. [43] used tomato as a model plant to investigate the effects of these two genes on fruit/seed set. They highlighted the crucial role of the miR393/TIR1 component in fruit/seed set and concluded that post-transcriptional regulation of these two genes mediated by miR393 is vital for fruit set initiation in both cucumber and tomato. The different stages of seed development and the structure of a dicot seed is presented in **Figure 1**.

**Figure 1.** *Different stages of seed development.*
