The expression pattern of dormancy-associated genes in multiple life-history stages in the rotifer Brachionus plicatilis

Rotifer resting eggs retain their viability for several decades in a non-desiccated form and are of interest in discerning the processes associated with dormancy, since in most organisms this phenomenon is linked with desiccation. The expression pattern of candidate genes with biological functions associated with dormancy in several other organisms was examined in rotifers. High-throughput transcriptome profiling revealed three patterns of gene expression in resting eggs: (1) relatively highly expressed genes coding for LEA proteins and putative paralogs of the small heat shock protein family (shsp); (2) genes coding for ferritin (ferr), glutathione-6-transferase (gts) and HSP70, where some of the putative gene paralogs of these families show relatively high expression levels and other putative paralogs show relatively low expression levels in resting eggs; and (3) genes with relatively low expression levels in resting eggs, for trehalose-6-phosphate synthase (tps), fatty-acid binding proteins (fab) and of lipoprotein lipase (lpl) and the aquaporins gene family (aqp). Changes in the expression pattern of some members of putative gene families occurred during the obligatory dormant period of resting eggs. A transition was observed from an expression pattern of diapausing embryos to an expression pattern of amictic females, during hatching. Differences were also found in the expression pattern in the different types of females, especially in those carrying resting eggs, and in males compared with females. These results suggest putative functional significance to genes associated with dormancy in non-desiccated resting eggs. It could also be proposed that their occurrence in resting eggs is developmentally programmed to facilitate survival in case of desiccation.