Two wrongs make a right: Heat stress reversion of a male-sterile Brassica napus line

Pollen development is considered the most heat susceptible developmental process in plants. Thus, the development of thermotolerant pollen is becoming an increasingly important economic trait in plant breeding. Here, a temperature-sensitive genic male sterility Brassica napus (TGMS) line is described, which, in contrast to most, displays fertility at higher temperatures. Also described are the male sterility and restorer of fertility genes for the male sterility Lembke (MSL) system used in rapeseed breeding in Europe. A specific and direct interaction between BnChimera and BnaC9-Tic40 in chloroplasts is demonstrated, indicating that this interaction may result in the restoration of male fertility in the presence of BnaC9-Tic40. Using an RNA-seq approach on untreated and heat-treated developing flowers suggested that the male sterile line may show a pre-treatment stress response, which is responsible for the thermotolerance of these lines. It is hypothesised that heat stress reverses the male sterility via a combination of slower production of cell wall precursors in chloroplasts and a slower flower development, which ultimately results in fertile pollen. The potential breeding applications of these results are discussed regarding the capacity of using the MSL system in producing thermotolerant fertile plants.