Large fruit of tomato Solanum lycopersicum L.: genetic determinants, organogenesis and fruit development (review)

Large fruit in Solanum lycopersicum L. is the result of domestication. We were interested in the appearance of large fruits in tomato in connection with the practice task to get new tomato forms with large fruits for multi-tiered hydroponic and aeroponic installations for vertical fruit production in greenhouses. Using the technology of target tomato breeding we obtained the first special dwarf tomato varieties Natasha and Timosha with small fruits for multi-tiered hydroponic installations. Obtaining of large fruit in tomato is connected with genetic and epigenetic control of the trait (An. Frary et al., 2000; B. Cong et al., 2006; Z. Huang et al., 2011; S. Wang, et al., 2011; A.J. Monforte et al., 2014; L. Azzi et al., 2015). The goal of this review is to summarize data on genetic determinants the trait of “size/weight of the fruit”, analysis processes of organogenesis, hormone and metabolic regulation of fruit development. Analysis of papers dedicated to fruit weight increasing during domestication shows the availability of 37 loci involved in regulation of cell division and enlargement at four different stages of fruit development, starting from the phases of ovary development and fruit set to the phases of cell development and enlargement of cells which form the mature fruit. Some of these loci are connected with processes of hormonal plant development at the phase of anthesis, fertilization, formation of fruits and seeds, and so, they are involved in auxin ( SlPIN4 , SlTIR1 , SlARF7 , SlARF8 , SlIAA9 ) and gibberellin ( SlGA20ox1 , SlDELLA1 ) signaling pathways. Others control cell enlargement during fruit development and maturing, and so, they are involved in regulation of primary ( HXK1 , SuSY , LIN5 , TIV1 , mMDH , cpFBP , SPA ) and secondary ( NOTABILIS / NCED1 , FLACCA , Gal-LDH , GME ) metabolism. Individual group of loci controls cell cycle at the period of ovary development ( TAGL1 , FAS , LC , SlWUS , SlIMA ) and fruit growth ( SlCDKA1 , SlCDCB1 , SlCDKB2 and SlCCS52A , SlWEE1 , SlKRP1 ) (L. Azzi et al., 2015). The fw2.2 is the first locus which has been described in detail (An. Frary et al., 2000). Locus fw2.2 controls the small fruit size in S. lycopersicum and is semidominant to allele FW2.2 of large fruit size. With transgenic lines, it had been established, that locus fw2.2 is carried by cos50. Sequence analysis of the cos50 had identified two open reading frames. One of them contain a single recombinant event, which delimited “the rightmost” end of the fw2.2 (XO33). Because genetic mutation(s) causing change in fruit size must be to the left of XO33, cDNA44 cannot be involved and open reading frame is the likely cause of the small-fruit phenotype. Next studies indicated that fw2.2 acts as a negative regulator of cell division during the very early stages of fruit development following pollination. Thus, fw2.2 is one of regulatory QTLs, such as achaete-scute , scabrous and Delta QTLs in fruit flies, teosinte-branched 1 ( tb1 ) in maize and Hox genes in animals (cited by B. Cong et al., 2006). Possible, locus FW2. 2 is positive regulator of cell division, which is involved in interaction with cytoplasmic membranes mediated by the regulatory (beta)-subunits of CKII kinase, that is well known in yeast and animals where it forms part of cell cycle related with signaling pathway (B. Cong et al., 2006).