AUTHOR=Zhang Yanfeng , Huang Shuhua , Wang Xuefang , Liu Jianwei , Guo Xupeng , Mu Jianxin , Tian Jianhua , Wang Xiaofeng 

TITLE=Defective APETALA2 Genes Lead to Sepal Modification in Brassica Crops

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00367

DOI=10.3389/fpls.2018.00367

ISSN=1664-462X

ABSTRACT=<p>Many vegetable and oilseed crops belong to <italic>Brassica</italic> species. The seed production of these crops is hampered often by abnormal floral organs, especially under the conditions of abiotic conditions. However, the molecular reasons for these abnormal floral organs remains poorly understood. Here, we report a novel pistil-like flower mutant of <italic>B. rapa</italic>. In the flower of this mutant, the four sepals are modified to one merged carpel that look like a ring in the sepal positions, enveloping some abnormal stamens and a pistil, and resulting in poor seed production. This novel mutant is named <italic>sepal-carpel modification</italic> (<italic>scm</italic>). DNA sequencing showed that the <italic>BrAP2a</italic> gene, the ortholog of <italic>Arabidopsis APETALA2</italic> (<italic>AP2</italic>) that specifies sepal identity, losses the function of in <italic>scm</italic> mutant due to a 119-bp repeated sequence insertion that resulted in an early transcription termination. <italic>BrAP2b</italic>, the paralog of <italic>BrAP2a</italic> featured two single-nucleotide substitutions that cause a single amino acid substitution in the highly conserved acidic serine-rich transcriptional activation domain. Each of the two <italic>BrAP2</italic> genes rescues the sepal defective phenotype of the <italic>ap2-5</italic> mutant of <italic>Arabidopsis</italic>. Furthermore, the knockout mutation of the corresponding <italic>BnAP2</italic> genes of oilseed rape (<italic>B. napus</italic>) by CRISPR/Cas9-mediated genome editing system resulted in <italic>scm</italic>-like phenotype. These results suggest that <italic>BrAP2</italic> gene plays a key role in sepal modification. Our finding provides an insight into molecular mechanism underlying morphological modification of floral organs and is useful for genetic manipulation of flower modification and improvement of seed production of <italic>Brassica</italic> crops.</p>