Promotion of Germination Using Hydroxamic Acid Inhibitors of 9-cis-Epoxycarotenoid Dioxygenase.

Abscisic acid (ABA) inhibits seed germination and the regulation of ABA biosynthesis has a role in maintenance of seed dormancy. The key rate-limiting step in ABA biosynthesis is catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED). Two hydroxamic acid inhibitors of carotenoid cleavage dioxygenase (CCD), D4 and D7, previously found to inhibit CCD and NCED in vitro, are shown to have the novel property of decreasing mean germination time of tomato (Solanum lycopersicum L.) seeds constitutively overexpressing LeNCED1. Post-germination, D4 exhibited no negative effects on tomato seedling growth in terms of height, dry weight, and fresh weight. Tobacco (Nicotiana tabacum L.) seeds containing a tetracycline-inducible LeNCED1 transgene were used to show that germination could be negatively and positively controlled through the chemical induction of gene expression and the chemical inhibition of the NCED protein: application of tetracycline increased mean germination time and delayed hypocotyl emergence in a similar manner to that observed when exogenous ABA was applied and this was reversed by D4 when NCED expression was induced at intermediate levels. D4 also improved germination in lettuce (Lactuca sativa L.) seeds under thermoinhibitory temperatures and in tomato seeds imbibed in high osmolarity solutions of polyethylene glycol. D4 reduced ABA and dihydrophaseic acid accumulation in tomato seeds overexpressing LeNCED1 and reduced ABA accumulation in wild type tomato seeds imbibed on polyethylene glycol. The evidence supports a mode of action of D4 through NCED inhibition, and this molecule provides a lead compound for the design of NCED inhibitors with greater specificity and potency.

Resequencing at ≥40-Fold Depth of the Parental Genomes of a Solanum lycopersicum × S. pimpinellifolium Recombinant Inbred Line Population and Characterization of Frame-Shift InDels That Are Highly Likely to Perturb Protein Function.

A recombinant in-bred line population derived from a cross between Solanum lycopersicum var. cerasiforme (E9) and S. pimpinellifolium (L5) has been used extensively to discover quantitative trait loci (QTL), including those that act via rootstock genotype, however, high-resolution single-nucleotide polymorphism genotyping data for this population are not yet publically available. Next-generation resequencing of parental lines allows the vast majority of polymorphisms to be characterized and used to progress from QTL to causative gene. We sequenced E9 and L5 genomes to 40- and 44-fold depth, respectively, and reads were mapped to the reference Heinz 1706 genome. In L5 there were three clear regions on chromosome 1, chromosome 4, and chromosome 8 with increased rates of polymorphism. Two other regions were highly polymorphic when we compared Heinz 1706 with both E9 and L5 on chromosome 1 and chromosome 10, suggesting that the reference sequence contains a divergent introgression in these locations. We also identified a region on chromosome 4 consistent with an introgression from S. pimpinellifolium into Heinz 1706. A large dataset of polymorphisms for the use in fine-mapping QTL in a specific tomato recombinant in-bred line population was created, including a high density of InDels validated as simple size-based polymerase chain reaction markers. By careful filtering and interpreting the SnpEff prediction tool, we have created a list of genes that are predicted to have highly perturbed protein functions in the E9 and L5 parental lines.