Karyotype and B chromosome variation in Lilium amabile Palibin

Karyomorphological and SEM studies in newly discovered populations of a critically endangered medicinal plant - Lilium polyphyllum D. Don ex Royle from a high altitude protected area of north-western Himalaya

In this study, new populations of a critically endangered Himalayan herb, Lilium polyphyllum D. Don ex Royle have been reported from Chamba, Himachal Pradesh, India for the first time. Karyotypic, palynological, and spermological studies under the light microscope (LM) and scanning electron microscope (SEM) have been carried out on specimens from these populations with an aim to add more knowledge to the current database of the species. Presently studied individuals depicted a diploid (2x) chromosome count of 2n = 24, which is in confirmation with the previous reports from Kashmir Himalaya. Mitotic study showed a karyotype formula of 2n = 2x = 2m + 2sm + 4st + 16t, that is, 2 metacentric +2 submetacentric +4 acrocentric +16 telocentric chromosomes. LM and SEM observations revealed that the pollen grains are monosulcate, heteropolar, elliptical in polar view, and oblate with reticulate ornamentation. Based on the criteria of number, shape, and arrangement of columellae that form the muri, pollen grains in L. polyphyllum correspond to Martagon type. This is the first SEM based study on pollen grains and seeds of endangered Himalayan white lily. Based on the present ecological data collected we confirm the status of L. polyphyllum to be critically endangered in the study area.

De novo transcriptome sequencing and gene expression profiling with/without B-chromosome plants of Lilium amabile

Supernumerary B chromosomes were found in Lilium amabile (2n = 2x = 24), an endemic Korean lily that grows in the wild throughout the Korean Peninsula. The extra B chromosomes do not affect the host-plant morphology; therefore, whole transcriptome analysis was performed in 0B and 1B plants to identify differentially expressed genes. A total of 154,810 transcripts were obtained from over 10 Gbp data by de novo assembly. By mapping the raw reads to the de novo transcripts, we identified 7,852 differentially expressed genes (log₂FC > |10|), in which 4,059 and 3,794 were up-and down-regulated, respectively, in 1B plants compared to 0B plants. Functional enrichment analysis revealed that various differentially expressed genes were involved in cellular processes including the cell cycle, chromosome breakage and repair, and microtubule formation; all of which may be related to the occurrence and maintenance of B chromosomes. Our data provide insight into transcriptomic changes and evolution of plant B chromosomes and deliver an informative database for future study of B chromosome transcriptomes in the Korean lily.

Cytological variations and long terminal repeat (LTR) retrotransposon diversities among diploids and B-chromosome aneuploids in Lilium amabile Palibin

BACKGROUND

B chromosomes are supernumerary chromosomes found in numerous plant species, including in the genus Lilium. Lilium amabile, an endemic Korean Lilium species, carries B chromosomes which are highly variable in terms of numbers and shape among the accessions collected throughout the Korea. Class 1 retrotransposons are highly abundant in the genome of Lilium species, but their biological functions are still obscure. Lilium species were known to hold high diversities derived from retrotransposons.

OBJECTIVE

In this study, genetic diversities among the L. amabile accessions were analyzed to better understand relationships between genetic variations and cytological diversities.

METHODS

Chromosomes were prepared from 95 L. amabile accessions for cytological identification. Genetic variations were analyzed by inter-retrotransposon amplified polymorphism (IRAP), and genetic differentiation was evaluated via Tajima's D neutrality and F_ST analyses. Population structure and phylogenetic analyses were also carried out.

RESULTS

The L. amabile accessions were classified into 11 cytotypes by the chromosome constitutions. Genetic diversity measured by IRAP analysis revealed high genetic diversity among the accessions. In the joint analysis of cytological variation with genetical variation, IRAP diversity was not related to the cytological diversities of diploid and aneuploids among L. amabile accessions, and genetic differentiation was not obvious. Moreover, the geographical distribution of L. amabile was not related to either IRAP diversity or cytological diversity.

CONCLUSION

The B chromosome-carrying aneuploids occurred randomly among diploids throughout Korea, and IRAP diversification predated L. amabile dispersion in Korea without genetic differentiation.