An R2R3 MYB Transcription Factor controlling Capsule Spine Formation in Castor

Castor (Ricinus communis L.) is a dicotyledonous oilseed crop that can have either spineless or spiny capsules. Spines are protuberant structures that differ from thorns or prickles. Until now, the development regulatory mechanisms governing spine formation in castor or other plants have remained largely unknown. Herein, using map-based cloning in two independent F2-LYY5/DL01 and F2-LYY9/DL01 populations, we have identified the RcMYB106 transcription factor as a key regulator of capsule spine development in Castor. Haplotype analyses demonstrate that either a 4353-bp deletion in the promoter or a SNP leading to a premature stop codon in the RcMYB106 gene could cause the spineless capsule phenotype in castor. Results of our biochemical experiment indicate that RcMYB106 might target a downstream gene RcWIN1, which encodes an ethylene response factor known to be involved in trichome formation in Arabidopsis, to control capsule spine development in Castor. This hypothesis, however, remains to be further tested. Nevertheless, our study reveals a potential molecular regulatory mechanism underlying the spine capsule trait in a non-model plant species.