Rapid Isolation of Loss of Function Mutations for Dominant Traits: A Case Study Using Photoperiod Response Gene in Cotton.

Besides their role in crop plant domestication, loss of function mutations are important resource for gene discovery, functional genomics and crop improvement. However, the isolation of loss of function mutations for traits that are dominant in inheritance requires the development of segregating progenies and phenotypic evaluation of M₂ plants of the mutagenesis populations. With a long crop growth cycle and unique seed processing requirements, development of mutant populations in cotton is time consuming and cumbersome. This becomes further complicated for trait evaluations that need special growth requirements for phenotyping such as specific photoperiod and temperature conditions. Tetraploid cotton wild species and land races are endemic to tropical and sub-tropical regions with short day lengths. Domesticated cotton is photoperiod insensitive while it is grown under long-day conditions in North America. Photoperiod sensitivity in wild and land races is a major barrier for the introgression of the tropical gene pool into the U.S. cotton-growing regions. Identification of genes controlling photoperiod response will be useful to efficiently introgress desirable genes from tropical germplasm. Here, we report on a method to rapidly isolate loss of function mutations in the dominant photoperiod response gene (GB_PPD1) using gamma rays on F₁ seeds that are heterozygous for the photoperiod response gene in Pima cotton (Gossypium barbadense). In addition, the characterization of the isolated mutations with molecular markers will be discussed.