Two tightly linked QTLs modify tomato sugar content via different physiological pathways

Abstract

Congenic lines that differ in a single defined chromosome segment are useful for the study of complex phenotypes, as they allow isolation of the effect of a particular quantitative trait locus (QTL) from those of the entire genome. We conducted high-resolution QTL mapping of a 9-cM introgression, originating from the wild tomato species Lycopersicon pennellii, in two extremely different genetic and physiological backgrounds. In the "indeterminate" glasshouse background we identified only a single QTL ( Brix9-2-5) that affects the total soluble solids of the fruit [mainly sugars, measured in Brix units (B)]. This QTL was previously delimited within the gene for an apoplastic invertase, Lin5, that modulates sugar partitioning to the fruit. Analysis of the effects of the same chromosome segment in "determinate", open-field tomatoes, revealed two QTLs, 0.3 cM apart: the fruit-specific Brix9-2-5 that affects B only, and the shoot-specific PW9-2-5, which accounts for an altered growth habit resulting in increases in plant weight, yield, and B. This study highlights the power of the congenic approach for dissecting developmental pathways leading to complex phenotypes.

Base genética do hábito de crescimento e florescimento em tomateiro e sua importância na agricultura

“…Como o hábito de crescimento regula, em última análise, o número relativo de folhas (fontes) com relação aos frutos (drenos), esse pode ter um grande impacto no brix. Dessa forma, as plantas de crescimento indeterminado (SP), as quais possuem mais folhas com relação ao número final de frutos, tendem a produzir frutos com brix mais elevado (32% maior) em relação às plantas de crescimento determinado (sp) (FRIDMAN et al, 2002).…”

“…Analogamente, as plantas de crescimento semi-determinado também possuem um brix superior (12,5%) às plantas de crescimento determinado (FRIDMAN et al, 2002), além de continuarem sendo mais adequadas para o cultivo mecanizado. Contudo, não está descartada a hipótese de que os genes da família SELF-PRUNING afetem o grau brix por um mecanismo bioquímico direto e não somente indiretamente, devido ao impacto no hábito de crescimento.…”

Advances in tomato research in the post-genome era

“…This property has been exploited for designing genetic markers and mapping populations (Eshed and Zamir 1995;Frary et al 2005;Lippman et al 2007), which have been the main driving force in marker-assisted selection for desirable traits such as fruit size (Frary et al 2000), ripening (Moore et al 2002), shape (Rodriguez et al 2011), sugar content (Fridman et al 2002), and resistance to biotic and abiotic stress (Labate and Robertson 2012;Verlaan et al 2013). Since virtually all heirloom tomatoes are disease susceptible, and have lost genetic diversity allowing for disease resistance (Bai and Lindhout 2007;Ranc et al 2012;Robbins et al 2011), modern plant breeding practices require introgressing the lost traits back from the wild relatives (Grandillo et al 2011), for example the bacterial resistance gene Pto was introgressed into tomato cultivars in the 1930s from Solanum pimpinellifolium (Lin and Martin 2007).…”

Growth habit in mini tomato hybrids from a dwarf line

“…Genotypes with three leaves and one inflorescence formed in each simpodial unit were classified as having the indeterminate growth habit (I); genotypes with two leaves and one inflorescence formed in each simpodial unit, with interruption of vegetative development in the main shoot to the formation of two consecutive inflorescences, were classified as having the semi-determinate growth habit (SD); and genotypes with three leaves and one inflorescence formed in the first simpodial unit, with gradual reduction of the number of leaves in subsequent units as well as interruption of vegetative development in the main shoot to the formation of two consecutive inflorescences, were classified as having the determined growth habit (D ) (FRIDMAN et al, 2002).…”

“…Compared to genotypes with indeterminate growth, in determinate growth is not necessary the accomplishment of onerous cultural practices such as sprout thinning, apical pruning and the conduct of plants with polythene strips or stakes (FILGUEIRA, 2008). However, the prioritization of the reproductive development among the vegetative can lead to a reduction in productivity and soluble solids content of the fruits in determinate genotypes (FRIDMAN et al, 2002). In contrast, semideterminate growth has an ideal balance between vegetative and reproductive development, having high productivity and high content of soluble solids in the fruits (VICENTE et al, 2015).…”