Sexual dimorphism and rapid turnover in gene expression in pre-reproductive seedlings of a dioecious herb

Sexual dimorphism in morphology, physiology or life history traits is common in dioecious plants at reproductive maturity, but it is typically inconspicuous or absent in juveniles. Although plants of different sexes probably begin to diverge in gene expression both before their reproduction commences and before dimorphism becomes readily apparent, it seems transcriptome-wide differential gene expression has yet to be demonstrated for any angiosperm species.

(A) Images of the typical (male) plant phenotype at each of the four growth stages studied. (B) Experimental design of Experiment 1 focusing on apical tissues. Three replicates have been produced per sex and per stage; each replicate is constituted of RNA extracted from ten pooled individuals. (C) Experimental design of Experiment 2, investigating mature leaves and root tissues. Five replicates have been produced per sex, per stage and per tissue; each replicate constituted of RNA extracted from a single individual. Blue circles and tubes represent male samples. Red circles and tubes represent female samples. The asterisk indicates that flowering occurred between Stage III and Stage IV.

Cossard, Toups and Pannell document differences in gene expression in both above- and below-ground tissues of early pre-reproductive individuals of the wind-pollinated dioecious annual herb, Mercurialis annua, which otherwise shows clear sexual dimorphism only at the adult stage.

The authors find sex-biased gene expression in M. annua occurs as early as the first whorl of leaves is produced, is highly dynamic during plant development and varies substantially between vegetative tissues.