ObjectiveThis study helped elucidate the molecular mechanism of polyploid phenotypic variation in sour jujube which can provide a reference for further study on jujube polyploidy traits, cloning of key regulatory genes and genetic engineering breeding.

MethodIn this study, Ziziphus jujuba Mill. var. spinosa and its autotetraploid were used as materials to compare the content of leaf relative water, chlorophyll, soluble sugar and soluble protein. The RNA-sequencing of these two materials was carried out. Functional classification and enrichment analysis of differentially expressed genes and transcription factors were performed by reference to GO Ontology, KEGG and others databases.

ResultThe chlorophyll content, soluble sugar content and soluble protein content in the autotetraploid were significantly higher than that in diploid. However, there was no obvious difference of the leaf relative water content between these two materials. There were 1 329 differentially expressed genes between diploid and its autotetraploid jujube. GO functional analysis indicated that these different genes were mainly involved in growth and stress tolerance. KEGG pathway analysis showed that the most of different genes were enriched in carbohydrate metabolism, amino acid metabolism and signal transduction process. Sixteen key genes such as SPS2, GAE6 and PGDH3 involving in the metabolism and transport of sugar and amino acids, exhibited higher expression level in the autotetraploid than that in diploid; 23 genes were involved in the plant hormone signaling pathway, in which genes related to auxin conduction and responses such as ARG7, GH3.6 and IAA26 were expressed highly in the autotetraploid plants, while genes related to brassinolide synthesis and ethylene-insensitive proteins showed lower expression level in the autotetraploid than that in diploid. In the analysis of different transcription factors, we found that the expression level of MYB transcription factor family genes was higher in the autotetraploid than that in diploid.

ConclusionHigh chlorophyll content resulted in darker leaves in the autotetraploid. High content of soluble sugar and soluble protein content provided more energy substances for autotetraploid to grow large leaves and thick stem. Many important genes encoding sugar and amino acids metabolism and plant hormone synthesis and signal transduction, were differentially expressed in diploid and its autotetraploid. This result may explain the traits of high energy content and strong growth potential of the autotetraploid plants. The highly expressed genes involved in osmotic adjustment in the autotetraploid suggest that the autotetraploid may be superior resistance than that of diploid. Further analysis of different transcription factors shows that the differential expression of MYB transcription factors between diploid and autotetraploid might lead to differences of plant growth and development, morphogenesis and stress resistance, but the specific performance in these materials need to be further investigated by experiments.