Abstract
The giant organs and enhanced concentrations of secondary metabolites realized by autopolyploidy are attractive for breeding the respective medicinal and agricultural plants and studying the genetic mechanisms. The traditional medicinal plant Chinese woad (Isatis indigotica Fort., 2n = 2x = 14) is now still largely used for the diseases caused by bacteria and viruses in China. In this study, its autopolyploids (3x, 4x) were produced and characterized together with the 2x donor for their phenotype and transcriptomic alterations by using high-throughput RNA sequencing. With the increase of genome dosage, the giantism in cells and organs was obvious and the photosynthetic rate was higher. The 4x plants showed predominantly the normal meiotic chromosome pairing (bivalents and quadrivalents) and equal segregation and then produced the majority of 4x progeny. The total 70136 All-unigenes were de novo assembled, and 56,482 (80.53%) unigenes were annotated based on BLASTx searches of the public databases. From pair-wise comparisons between transcriptomic data of 2x, 3x, 4x plants, 1856 (2.65%)(2x vs 4x), 693(0.98%)(2x vs 3x), 1045(1.48%)(3x vs 4x) unigenes were detected to differentially expressed genes (DEGs), including both up- and down-regulated ones. These DEGs were mainly involved in cell growth (synthesis of expansin and pectin), cell wall organization, secondary metabolite biosynthesis, response to stress and photosynthetic pathways. The up-regulation of some DEGs for metabolic pathways of functional compounds in the induced autotetraploids substantiates the promising new type of this medicinal plant with the increased biomass and targeted metabolites.
Highlights
Polyploidy which contributed greatly to the evolution of angiosperms is involved in the speciation of many important crops, such as the autopolyploids alfalfa and potato or more frequent allopolyploids bread wheat, cotton, oilseed rape, coffee, etc. [1, 2]
The results from tetraploidizing various Arabidopsis thaliana mutants and transgenics with a wide range in cell size indicated that the ploidy-dependent increase in cell volume is genetically regulated [6]
The knowledge that the polyploidy related giantism was attributed to the ploidydependent cell enlargement, not to the more cell number has been obtained and widely accepted for fungi, plants, and animals [2, 4, 5, 6, 46, 47]
Summary
Polyploidy which contributed greatly to the evolution of angiosperms is involved in the speciation of many important crops, such as the autopolyploids alfalfa and potato or more frequent allopolyploids bread wheat, cotton, oilseed rape, coffee, etc. [1, 2]. The results from tetraploidizing various Arabidopsis thaliana mutants and transgenics with a wide range in cell size indicated that the ploidy-dependent increase in cell volume is genetically regulated [6]. Study reported that the chloroplast number and photosynthesis per cell all increase with ploidy increase, which were attributed to increased size of cells [7]. The recent experiment showed that not the nuclear ploidy but the cell area was the key parameter determining the activity of chloroplast proliferation, while the expression of the related genes was not promoted in the lines with the defect in cell proliferation but enhanced post-mitotic cell expansion [8]. The mechanisms behind the ploidy-related regulation of cell size, cell proliferation and expansion, cellular proliferation remain largely for further studies [8]
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