Dissecting the genetic architecture of salt tolerance in the wild tomato Solanum pimpinellifolium

Abstract

Salt stress severely constrains plant performance and global agricultural productivity. 5% of arable land, 20% of irrigated areas and 98% of water reserves worldwide are saline. Improving the salt tolerance of major crop species could help attenuate yield losses and expand irrigation opportunities and provide in situ relief in areas where poverty, food and water scarcity are prevalent. Increasing the salt tolerance of crops with high commercial and nutritional value, such as tomato (Solanum lycopersicum L.), would provide particularly significant economic and health benefits. However, salt tolerance is a complex trait with a limited genetic repertoire in domesticated crop varieties, including tomato, frustrating attempts to breed and engineer tolerant crop varieties. Here, a genome-wide association study (GWAS) was undertaken, leveraging the rich genetic diversity of the wild, salt tolerant tomato Solanum pimpinellifolium and the latest phenotyping technologies to identify traits that contribute to salt tolerance and the genetic basis for variation in those traits. A panel of 220 S. pimpinellifolium accessions was phenotyped, focusing on image-based high-throughput phenotyping over time in controlled and field conditions in young and mature plants. Results reveal substantial natural variation in salt tolerance over time across many traits. In particular, the use of unmanned aerial vehicle (UAV)-based remote sensing in the field allowed high-resolution RGB, thermal and hyperspectral mapping that offers new insights into plant performance in the field, over time. To empower our GWAS and facilitate the identification of candidate genes, a new S. pimpinellifolium reference genome was generated, 811Mb in size, N50 of ~76kb, containing 25,970 annotated genes. Analysis of this reference genome highlighted potential contributors to salt tolerance, including enrichments in genes with stress response functions and a high copy number of the salt tolerance-associated gene inositol- 3-phosphate synthase (I3PS). A recently completed full genome re-sequencing of the panel, along with a newly available pseudomolecule-level assembly of the S. pimpinellifolium genome with N50 of ~11Mb, will serve to drive a GWAS to identify loci associated with traits that contribute to salt tolerance. Further research including gene validation, breeding, genetic modification and gene editing experiments will drive the development of new salt tolerant tomato cultivars.

Date of Award	Oct 2019
Original language	English (US)
Awarding Institution	Biological, Environmental Sciences and Engineering
Supervisor	Mark Tester (Supervisor)