BrSPA1 mutation resulted in earlier bolting of Chinese cabbage under short day conditions

Bolting, a considerable trait of Chinese cabbage, affects its regional adaptation and is associated with leafy-head yield, especially for the edible stalk type of Chinese cabbage. In this study, an earlier bolting mutant ebm12 derived from an Ethyl Methane Sulfonate mutagenesis population was selected as material and its flowering time was approximately 19 days earlier than that of its wild-type (WT) in SD. Genetic analysis proved that the earlier bolting characteristic was controlled by a single recessive nuclear gene. A light responsive repressor of photomorphogenesis gene BraA05g001450.3C was identified as the candidate for BrSPA1 by MutMap analysis and co-segregated test (Kompetitive Allele Specific PCR, KASP). DNA sequencing revealed that the mutation in the first exon of BraA05g001450.3C generated the premature termination and the loss of functionally conserved domain. qRT-PCR revealed that the earlier bolting of ebm12 under SD conditions could be associated with high FT and low HFR1 transcription levels. BrSPA1 mutation promoted earlier bolting under SD conditions rather than under LD conditions, meaning that BrSPA1 mutation transformed the photoperiodic characteristics of Chinese cabbage. The SD bolting mutant ebm12 could be applied to breed edible stalk type of Chinese cabbage.