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.
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.
Cossard, G. G., Toups, M. A., & Pannell, J. R. (2018). Sexual dimorphism and rapid turnover in gene expression in pre-reproductive seedlings of a dioecious herb. Annals of Botany. https://doi.org/10.1093/aob/mcy183