Long-Read cDNA Sequencing Revealed Novel Expressed Genes and Dynamic Transcriptome Landscape of Triticale (x Triticosecale Wittmack) Seed at Different Developing Stages

Developing seed is a unique stage of plant development with highly dynamic changes in transcriptome. Here, we aimed to detect the novel previously unannotated, genes of the triticale (x Triticosecale Wittmack, AABBRR genome constitution) genome that are expressed during different stages and at different parts of the developing seed. For this, we carried out the Oxford Nanopore sequencing of cDNA obtained for middle (15 days post-anthesis, dpa) and late (20 dpa) stages of seed development. The obtained data together with our previous direct RNA sequencing of early stage (10 dpa) of seed development revealed 39,914 expressed genes including 7128 (17.6%) genes that were not previously annotated in A, B, and R genomes. The bioinformatic analysis showed that the identified genes belonged to long non-coding RNAs (lncRNAs), protein-coding RNAs, and TE-derived RNAs. The gene set analysis revealed the transcriptome dynamics during seed development with distinct patterns of over-represented gene functions in early and middle/late stages. We performed analysis of the lncRNA genes polymorphism and showed that the genes of some of the tested lncRNAs are indeed polymorphic in the triticale collection. Altogether, our results provide information on thousands of novel loci expressed during seed development that can be used as new targets for GWAS analysis, the marker-assisted breeding of triticale, and functional elucidation.