Abstract
A mutant line, bifurcate flower truss (bif), was recovered from a tomato genetics programme. Plants from the control line produced a mean of 0.16 branches per truss, whereas the value for bif plants was 4.1. This increase in branching was accompanied by a 3.3-fold increase in flower number and showed a significant interaction with exposure to low temperature during truss development. The control line and bif genomes were resequenced and the bif gene was mapped to a 2.01 Mbp interval on chromosome 12; all coding region polymorphisms in the interval were surveyed, and five candidate genes displaying altered protein sequences were detected. One of these genes, SlMAPK1, encoding a mitogen-activated protein (MAP) kinase, contained a leucine to stop codon mutation predicted to disrupt kinase function. SlMAPK1 is an excellent candidate for bif because knock-out mutations of an Arabidopsis orthologue MPK6 were reported to have increased flower number. An introgression browser was used to demonstrate that the origin of the bif genomic DNA at the BIF locus was Solanum galapagense and that the SlMAPK1 null mutant is a naturally occurring allele widespread only on the Galápagos Islands. This work strongly implicates SlMAPK1 as part of the network of genes controlling inflorescence branching in tomato.
Highlights
Inflorescence architecture and the number of flowers produced per plant are controlled by an extensive network of genes in the Solanaceae family (Lemmon et al, 2016)
Considering the mean of the first two trusses, bif produced 39.8 ± 1.6 flowers per truss, which was 3.3-fold higher than the 12.0 ± 0.3 flowers per truss exhibited by LAM183 (Table 1).The number of truss branch points was affected—bif trusses showed a mean of 4.1 ± 1.8 branch points per truss compared with 0.16 ± 0.37 in LAM183, representing a 25.6-fold difference
Inflorescence branching was not reported in these QTL studies, and there were apparently no other major morphological QTLs reported to be associated with the Solyc12g019460 null mutation present in LA0483; this is agreement with the observation here that there were no major effects on plant development other than inflorescence branching and flower number when comparing the LAM183 and bif lines
Summary
Inflorescence architecture and the number of flowers produced per plant are controlled by an extensive network of genes in the Solanaceae family (Lemmon et al, 2016). An increase in the number of flowers will lead to a greater fruit yield provided that reproductive growth is limited by sink strength rather than by assimilate supply (Périlleux et al, 2014). Production of more flowers than the assimilate supply can sustain is a waste of resources and may negatively affect final fruit yield. Where assimilate supply is limiting, fruit number is inversely proportional to fruit size and is regulated by flower and fruit abscission in response to endogenous and environmental signals (Saglam and Yazgan, 1999). In fleshy fruit crops such as Solanum lycopersicum (tomato), growers manage fruit size and uniformity by thinning and pruning (Cockshull and Ho, 1995; Max et al, 2016).
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