Abstract
BackgroundPolyploid plants often exhibit enhanced stress tolerance. The underlying physiological and molecular bases of such mechanisms remain elusive. Here, we characterized the drought tolerance of autotetraploid sour jujube at phenotypic, physiological and molecular levels.ResultsThe study findings showed that the autotetraploid sour jujube exhibited a superior drought tolerance and enhanced regrowth potential after dehydration in comparison with the diploid counterpart. Under drought stress, more differentially expressed genes (DEGs) were detected in autotetraploid sour jujube and the physiological responses gradually triggered important functions. Through GO enrichment analysis, many DEGs between the diploid and autotetraploid sour jujube after drought-stress exposure were annotated to the oxidation–reduction process, photosystem, DNA binding transcription factor activity and oxidoreductase activity. Six reactive oxygen species scavenging-related genes were specifically differentially expressed and the larger positive fold-changes of the DEGs involved in glutathione metabolism were detected in autotetraploid. Consistently, the lower O2− level and malonaldehyde (MDA) content and higher antioxidant enzymes activity were detected in the autotetraploid under drought-stress conditions. In addition, DEGs in the autotetraploid after stress exposure were significantly enriched in anthocyanin biosynthesis, DNA replication, photosynthesis and plant hormone, including auxin, abscisic acid and gibberellin signal-transduction pathways. Under osmotic stress conditions, genes associated with the synthesis and transport of osmotic regulators including anthocyanin biosynthesis genes were differentially expressed, and the soluble sugar, soluble protein and proline contents were significantly higher in the autotetraploid. The higher chlorophyll content and DEGs enriched in photosynthesis suggest that the photosynthetic system in the autotetraploid was enhanced compared with diploid during drought stress. Moreover, several genes encoding transcription factors (TFs) including GRAS, Bhlh, MYB, WRKY and NAC were induced specifically or to higher levels in the autotetraploid under drought-stress conditions, and hub genes, LOC107403632, LOC107422279, LOC107434947, LOC107412673 and LOC107432609, related to 18 up-regulated transcription factors in the autotetraploid compared with the diploid were identified.ConclusionTaken together, multiple responses contribute to the enhanced drought tolerance of autotetraploid sour jujube. This study could provide an important basis for elucidating the mechanism of tolerance variation after the polyploidization of trees.
Highlights
Polyploid plants often exhibit enhanced stress tolerance
Taken together, multiple responses contribute to the enhanced drought tolerance of autotetraploid sour jujube
Autotetraploid sour jujube shows superior drought tolerance compared with the diploid counterpart To study the drought tolerance of autotetraploid compared with diploid sour jujube, 60 diploids and 60 autotetraploids were subjected to 21 days of drought stress and 40 days of rehydration treatment
Summary
Polyploid plants often exhibit enhanced stress tolerance. The underlying physiological and molecular bases of such mechanisms remain elusive. We characterized the drought tolerance of autotetraploid sour jujube at phenotypic, physiological and molecular levels. Plants are exposed to harsh environmental conditions, including low and high temperatures, drought and salinity. Under drought-stress conditions, significant changes in cell physiology and biochemistry occur, including decreases in turgor pressure, changes in the plasma membrane composition and fluidity, and changes in cell solute concentration and protein–lipid interactions [5]. Large numbers of physiological and metabolic pathways undergo changes, including decreases in photosynthetic activity, accumulations of organic acids and osmotic regulators, changes in carbohydrate metabolism, increases in protein-protective complex synthesis, enhanced energy and lipid metabolism, and the removal of reactive oxygen species (ROS), to adapt to a drought environment [6, 7]. The sensing and inward transduction of the drought signals by the corresponding receptors on the cell membrane lead to gene expression and transcription factor regulation, which effect the expression of corresponding functional proteins
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