Comparative phenotypic and transcriptomic analyses reveal the potential molecular basis of forming bigger leaf blade...

Whole-genome duplication events often confer autopolyploid plants with bigger leaf blades compared with those of their diploid counterparts. However, little is known regarding the potential molecular basis of bigger leaf formation in autopolyploid plants. Here, we focused on the oilseed crop castor bean (Ricinus communis L.) to investigate the molecular basis underlying leaf size variation using a synthetic autotetraploid by doubling the diploid homologous chromosomes.

The results showed that the leaf area of autotetraploids was significantly larger than that of diploids. According to our histological observations, the formation of larger leaf blades in tetraploid castor beans is attributed to both an increase in cell size and an increase in cell number. A total of 3,464 differentially expressed genes (DEGs) between diploids and tetraploids were identified by RNA sequencing analysis. The expression of key genes related to cell wall loosening, cell expansion and cell division was higher in tetraploid leaf blades compared to diploids, resulting in enlarged tetraploid leaf blades, such as SUS2, SUS4, XYL1, Xyl2, XTH30, XTH32, EXPA1, EXPA4, EXPA6, EXPB3, CYCD3;1 and CYCD3;3 were significantly up-regulated in tetraploids. Concurrently, auxin-responsive genes (SAUR20, SAUR23, and SAUR51) in the auxin signaling pathway showed significant up-regulated in tetraploids, facilitating leaf cell expansion. Transcription factors (TFs) including HAT22, SRM1, ERF4, and DOF3.4 likely regulate cell expansion and elongation pathways, ultimately driving the enlargement of tetraploid leaf blades.

Our findings provide important insight into understanding the potential molecular basis of gene dosage effects on trait variation in autopolyploid plants.