Cichorium intybus L.?×?Cicerbita alpina Walbr.: doubled haploid chicory induction and CENH3 characterization
Intergeneric hybridization between industrial chicory (Cichorium intybus L.) and Cicerbita alpina Walbr. induces interspecific hybrids and haploid chicory plants after in vitro embryo rescue. The protocol yielded haploids in 5 out of 12 cultivars pollinated; altogether 18 haploids were regenerated from 2836 embryos, with a maximum efficiency of 1.96% haploids per cross. Obtained haploids were chromosome doubled with mitosis inhibitors trifluralin and oryzalin; exposure to 0.05 g L-1 oryzalin during one week was the most efficient treatment to regenerate doubled haploids. Inbreeding effects in vitro were limited, but the ploidy level affects morphology. Transcriptome sequencing revealed two unique copies of CENH3 in Cicerbita alpina Walbr. Comparison of CENH3.1 protein sequences of Cicerbita and Cichorium obtained through transcriptome and whole shotgun genome sequencing revealed two amino-acid substitutions at critical residues of the histone fold domain. These particular changes cause chromosome elimination and reduced centromere loading in several other species and might indicate a CENH3-dependent mechanism causing chromosome elimination of parental chromosomes during Cichorium?×?Cicerbita intergeneric hybridization. Our results provide insights in chromosome elimination and might increase the efficiency of haploid induction in Cichorium.