Identification of genes involved in lettuce seed thermoinhibition
Germination of lettuce (Lactuca sativa
) seeds is delayed or inhibited when planted at warm temperatures, leading to delays or failures in germination and seedling emergence and resulting in yield losses and higher costs. The Bradford lab in collaboration with the Michelmore lab previously identified a quantitative trait locus (QTL) that regulates the temperature sensitivity of germination and subsequently demonstrated that a gene (LsNCED4
) encoding an enzyme in the biosynthetic pathway for abscisic acid (ABA) is responsible for the trait. A second QTL from a different genetic source that also improves germination at high temperatures is currently being fine-mapped and characterized by PhD student Fei-Yian Yoong
. Postdoctoral scholar Heqiang Huo
and visiting scientist Shouhui Wei
discovered that a gene previously known to be involved in regulating seed dormancy (termed DELAY OF GERMINATION 1
) is also involved in regulating seed thermoinhibition. This research has been supported by the National Science Foundation, USDA-National Institute of Food and Agriculture, and the Chinese Academy of Agricultural Sciences.Effects of maternal environment during seed development on lettuce seed thermoinhibition?
As noted above, cultivated lettuce seeds generally lack the ability to germinate at warm temperatures. However, the upper temperature limit for germination is sensitive to the environment in which the seeds were produced: seeds matured at warm temperatures can germinate at higher temperatures than seeds matured at lower temperatures. PhD student Mohan Niroula in the Bradford lab is seeking to identify the genetic mechanisms responsible for this environmental plasticity with the goal of making seed performance more consistent and less dependent upon the location of seed production. By producing seeds of a genetic mapping population in a number of different environments, he has been able to identify a QTL associated with this environmental effect on seed germination capacity at high temperature. This work is supported by the Western Regional Seed Physiology Research Group, a consortium of seed and seed technology companies (Ball Horticultural, Bejo Zaden, East-West Seeds, Enza Zaden, Germain’s Technology Group, HM.Clause, INCOTEC, Monsanto Vegetable Seeds, Nunhems USA, Rijk Zwaan, Sakata Seed America, Seed Dynamics and Syngenta).
Identification of mutations affecting lettuce seed thermoinhibition by genomic sequencing
With support from Rijk Zwaan, postdoc Heqiang Huo
and visiting scientist Shouhui Wei
of the Bradford lab collaborated with the Luca Comai
lab in the UC Davis Genome Center to test a new strategy to identify mutations affecting seed germination. Rijk Zwaan scientists induced mutations in lettuce and selected lines that resulted in germination at higher temperatures. Using a method called bulked segregant analysis (BSA), a segregating population of seedlings was separated into groups that either did or did not germinate at high temperature. Total genomic DNA from the selected pools was sequenced, and comparisons of differences in the sequences enabled the identification of the mutated gene that affected germination. This project demonstrated that this BSA by sequencing approach was feasible for identifying specific mutations even in a large genome such as lettuce (2.7 billion base pairs).