A comparative morphological and transcriptomic study on autotetraploid Stevia rebaudiana (bertoni) and its diploid

Stevia rebaudiana is an important medical plant for producing steviol glycosides (SGs) or stevioside. Autotetraploids (4x = 44) show an increasing level of morphology, physiology and tolerances comparing to diploids (2x = 22). However, little information regarded on the comparative transcriptome analysis between diploid and autotetraploid S. rebaudiana was found. In this study, synthetic autotetraploid was induced and morphological features were confirmed. A comprehensive transcriptome of stevia leaf, stem and root from the diploids and autotetraploids was constructed based on RNA-seq, yielded 1,000,892,422 raw reads and subsequently assembled into 251,455 transcripts, corresponded to 146,130 genes. Pairwise comparisons of the six leaf libraries between the diploids and autotetraploids revealed 4114 differentially expression genes (DEGs), in which 2105 (51.17%) were up-regulated in autotetraploids and associated with SGs biosynthesis, plant growth and secondary metabolism. Moreover, weighted gene co-expression network analysis showed co-expressed genes of fifteen genes of SG biosynthesis pathway were enriched in photosynthesis, flavonoid and secondary metabolic process, plant growth and morphogenesis. A hundred of DEGs related to plant resistance were identified by interviewing PlantPReS database. This study has highlighted molecular changes related to SGs metabolism of polyploidy, and advanced our understanding in plant resistance responsible for phenotypic change of autotetraploids.