Abstract
Aneuploidy with loss of entire chromosomes from normal complement disrupts the balanced genome and is tolerable only by polyploidy plants. In this study, the monosomic and nullisomic plants losing one or two copies of C2 chromosome from allotetraploid Brassica napus L. (2n = 38, AACC) were produced and compared for their phenotype and transcriptome. The monosomics gave a plant phenotype very similar to the original donor, but the nullisomics had much smaller stature and also shorter growth period. By the comparative analyses on the global transcript profiles with the euploid donor, genome-wide alterations in gene expression were revealed in two aneuploids, and their majority of differentially expressed genes (DEGs) resulted from the trans-acting effects of the zero and one copy of C2 chromosome. The higher number of up-regulated genes than down-regulated genes on other chromosomes suggested that the genome responded to the C2 loss via enhancing the expression of certain genes. Particularly, more DEGs were detected in the monosomics than nullisomics, contrasting with their phenotypes. The gene expression of the other chromosomes was differently affected, and several dysregulated domains in which up- or downregulated genes obviously clustered were identifiable. But the mean gene expression (MGE) for homoeologous chromosome A2 reduced with the C2 loss. Some genes and their expressions on C2 were correlated with the phenotype deviations in the aneuploids. These results provided new insights into the transcriptomic perturbation of the allopolyploid genome elicited by the loss of individual chromosome.
Highlights
The aneuploidy for one species refers to the occurrence of one or more extra or missing chromosomes in the normal number (2n) in the cells, leading to an unbalanced chromosome complement
The deviation in morphology and flowering habitat suggested that the missing chromosome pair in the nullisomics carried the genes controlling the plant height and vernalization in B. napus
Their pollen mother cells (PMCs) showed normal chromosome pairing with 18 bivalents at diakinesis and predominantly equal 18:18 segregations at anaphase I (AI) (Figure S1), and unequal 17:19 segregations at low frequency
Summary
The aneuploidy for one species refers to the occurrence of one or more extra or missing chromosomes in the normal number (2n) in the cells, leading to an unbalanced chromosome complement. Transcriptome in Brassica aneuploids (monosomy) is usually lethal for animals and diploid plants, but the gain of one (trisomy) or two (tetrasomy) copies of one chromosome is tolerable (Siegel and Amon, 2012). The complete series of monosomics and even nullisomics with the loss of one specific chromosome pair have been successfully established in some important allopolyploid crops, including the allohexaploid common wheat (Triticum aestivum L.), for the closely related genomes in the allopolyploid species from different progenitors can compensate functionally each other (Sears, 1954). The genetic study of the aneuploids contributes greatly to our early understanding of genome structure and homoeologous relationships between the different genomes in allopolyploids (Sears, 1954) and to the chromosome-based sequencing of the very large wheat genome (Mayer et al, 2014)
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