Domestication of Tomato

Solanum lycopersicum is the tomato species that we are most familiar with and that has been domesticated (Tanksley, 2004; Koenig et al., 2013). The exact domestication site of tomato is unknown but is thought to be placed in Mexico or Peru (Bai and Lindhout, 2007; Bergougnoux, 2014). On the other hand, what is known is that his domestication was a two-step process (Fig. 1) (Lin et al., 2014; Blanca et al., 2015). 

These two steps determine the domestication and improvement sweeps, that consist in the increase of the frequency of a certain allele and the hitchhiking genes nearby, in the population (Schaffner and Sabeti, 2008; Lin et al., 2014). 

The main phenotypic changes are the fruit size and shape and the seed size and weight (Bai and Lindhout, 2007). 8 There are 5 QTL (fw1.1, fw5.2, fw7.2, fw12.1 and lcn12.1) related to the first step of domestication involved in the increase of the fruit size and another 13 QTL (fw2.1, fw2.2, fw2.3, lcn2.1, lcn2.2, fw3.2, lcn3.1, fw9.1, fw9.3, lcn10.1, fw11.1, fw11.2, and fw11.3) involved in the second step (Lin et al., 2014). fw2.2, or fruit weight2.2, is one of the best-characterized QTL involved in the fruit size (Frary, 2000; Cong et al., 2002; Bai and Lindhout, 2007; Paran and van der Knaap, 2007).

The locis controlling the fruit size and shape are not totally separated things (Tanksley, 2004). ovate, sun and fs8.1 are the principals loci controlling the fruit shape, this QTL differ in their physiological effects and in their way of acting, ranging from pear-shape (ovate) to square tomatoes (fs8.1) and by acting after pollination (sun) to begin in the floral/carpel development (fs8.1) (Tanksley, 2004; Brewer et al., 2007; Paran and van der Knaap, 2007). The seed characteristics also change (by sw4.1, for example), being bigger in the domesticated crop due to a selective pressure related to breeding objectives (Bai and Lindhout, 2007).

Figure 1- Two-step evolution of tomato and the quantitative trait locus inherent to each step. PIM refers to S. pimpinellifolium; CER to S. lycopersicum var. cerasiforme; and BIG to S. lycopersicum. From Lin et al., (2014).

Bibligraphy

Bai, Y. and Lindhout, P. (2007). Domestication and Breeding of Tomatoes: What have We Gained and What Can We Gain in the Future? Annals of Botany, 100(5), pp.1085-1094.

Bergougnoux, V. (2014). The history of tomato: From domestication to biopharming. Biotechnology Advances, 32(1), pp.170-189.

Blanca, J., Montero-Pau, J., Sauvage, C., Bauchet, G., Illa, E., Díez, M., Francis, D., Causse, M., van der Knaap, E. and Cañizares, J. (2015). Genomic variation in tomato, from wild ancestors to contemporary breeding accessions. BMC Genomics, 16(1).

Brewer, M., Moyseenko, J., Monforte, A. and van der Knaap, E. (2007). Morphological variation in tomato: a comprehensive study of quantitative trait loci controlling fruit shape and development. Journal of Experimental Botany, 58(6), pp.1339-1349.

Cong, B., Liu, J. and Tanksley, S. (2002). Natural alleles at a tomato fruit size quantitative trait locus differ by heterochronic regulatory mutations. Proceedings of the National Academy of Sciences, 99(21), pp.13606-13611.

Frary, A. (2000). fw2.2: A Quantitative Trait Locus Key to the Evolution of Tomato Fruit Size. Science, 289(5476), pp.85-88.

Koenig, D., Jimenez-Gomez, J., Kimura, S., Fulop, D., Chitwood, D., Headland, L., Kumar, R., Covington, M., Devisetty, U., Tat, A., Tohge, T., Bolger, A., Schneeberger, K., Ossowski, S., Lanz, C., Xiong, G., TaylorTeeples, M., Brady, S., Pauly, M., Weigel, D., Usadel, B., Fernie, A., Peng, J., Sinha, N. and Maloof, J. (2013). Comparative transcriptomics reveals patterns of selection in domesticated and wild tomato. Proceedings of the National Academy of Sciences, 110(28), pp.E2655-E2662.

Lin, T., Zhu, G., Zhang, J., Xu, X., Yu, Q., Zheng, Z., Zhang, Z., Lun, Y., Li, S., Wang, X., Huang, Z., Li, J., Zhang, C., Wang, T., Zhang, Y., Wang, A., Zhang, Y., Lin, K., Li, C., Xiong, G., Xue, Y., Mazzucato, A., Causse, M., Fei, Z., Giovannoni, J., Chetelat, R., Zamir, D., Städler, T., Li, J., Ye, Z., Du, Y. and Huang, S. (2014). Genomic analyses provide insights into the history of tomato breeding. Nature Genetics, 46(11), pp.1220- 1226.

Paran, I. and van der Knaap, E. (2007). Genetic and molecular regulation of fruit and plant domestication traits in tomato and pepper. Journal of Experimental Botany, 58(14), pp.3841-3852.

Schaffner, S. and Sabeti, P. (2008) Evolutionary adaptation in the human lineage. Nature Education, 1(1):14.

Tanksley, S. (2004). The Genetic, Developmental, and Molecular Bases of Fruit Size and Shape Variation in Tomato. THE PLANT CELL ONLINE, 16(suppl_1), pp.S181-S189.