Hybridization in plants combines different genomes in the same cell, and
genome "shock" and instability occur during this process. Chromosome
doubling then reconstructs the genome dosage. Recent studies have shown that
small RNAs play an important role in maintaining genome stability. However,
little is known of small RNA's role during wide hybridization and chromosome
doubling. Therefore, Liping Chen of Zhejiang University in China studied the
genetic and DNA methylation alterations and changes in the siRNA and miRNA
during the formation of the allodiploid and allotetraploid between Brassica
rapa and Brassica nigra.

The expression of miRNAs increased in the allodiploid and allotetraploid
compared with the parents, while the levels of siRNAs was found higher
compared to B. rapa but lower compared with B. nigra. As the polyploidy
increases, the levels of miRNAs increased, suggesting its role in regulating
gene expression. On the other hand, levels of siRNAs and DNA methylation
alterations decreased as the ploidy increased and become more stable. These
results may provide new information for understanding that the
allotetraploids have a growth advantage over the parents and the
allodiploids.

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