Several vegetable and oilseed crops belong to Brassica species. The seed
production of these crops is often affected by abnormal flowers, especially
under the unfavorable abiotic conditions. However, the molecular reasons for
these abnormal floral organs remain unknown.



A team led by Yanfeng Zhang from the Hybrid Rapeseed Research Center in
China aims to shed light on this by studying a flower mutant of turnip
(Brassica rapa). In the flower of this mutant, named sepal-carpel
modification (scm), the four sepals are modified to one merged carpel that
look like a ring, enveloping abnormal stamens and a pistil, and resulting in
poor seed production.



DNA analysis of the mutant showed that the BrAP2a gene, the ortholog of
Arabidopsis APETALA2 (AP2) that specifies sepal identity, lost its function
in the scm mutant due to an insertion. Furthermore, the CRISPR-Cas9-knockout
of the two BnAP2 genes, BrAP2a, and its ortholog BrAP2b, in oilseed rape
(Brassica napus) resulted in scm-like phenotype, suggesting that BrAP2 plays
a key role in sepal modification.

These findings could provide an insight into the morphological modification
of floral organs and will be useful for improvement of seed production of
Brassica crops.



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