Insights into the caleosin family in Cyperus esculentus, an oil-rich tuber plant in Cyperaceae

Background Caleosins (CLOs), a class of structural proteins of lipid droplets (LDs), widely function in LD formation, stabilization, and degradation as well as in plant development and stress responses. However, their characterization in tigernut ( Cyperus esculentus L., Cyperaceae), a rare example accumulating significant amounts of oil in underground tubers, is still in the infancy. Results In this study, we present a first genome-wide analysis of the caleosin family in tigernut. A number of eight members, which represent two previously defined clades (i.e., H and L), were identified from the tigernut genome, in stark contrast to only two present in the basal angiosperm Amborella trichopoda . Comparison of 193 caleosin genes from 31 representative plant species reveals lineage-specific expansion and functional diversification. Eight CeCLO genes belong to eight out of 11 orthogroups identified in this study, and extensive expansion in this species was contributed by whole-genome duplication (WGD), tandem, and dispersed duplications. 1:1 orthologous relationships observed between tigernut and its close relative Cyperus rotundus suggest that gene copies are not the contributor of high tuber oil accumulation in tigernut. Instead, most CeCLO genes was shown to express more than their orthologs in C. rotundus , implying species-specific activation in oil-bearing tigernut tubers. Correspondingly, expression of CeCLO1 , -2 , -3 , and − 7 was shown to positively correlate with oil accumulation during tuber development. Structure and expression divergence of paralogous pairs were also observed, and good examples are 1) CeCLO7 and − 8 that have gained one additional intron and 2) CeCLO1 that has become the predominant isoform in oil-rich tubers. Conclusions These findings provide insights into the evolution, expression, and structural variation of CeCLO genes, which improve our knowledge on the mechanism of high oil accumulation in tigernut tubers.