Heterochronic reproductive developmental processes between diploid and tetraploid cytotypes of Paspalum rufum

SOLIMAN, MARIANO; DELGADO, LUCIANA; ORTIZ, JUAN PABLO A; ESPINOZA, FRANCISCO; SOLIMAN, MARIANO; DELGADO, LUCIANA; ORTIZ, JUAN PABLO A; ESPINOZA, FRANCISCO

ANNALS OF BOTANY

OXFORD UNIV PRESS

Año: 2019 vol. 123 p. 901 - 915

0305-7364

Background and Aims: Apomixis is an asexual reproductive mode via seeds that generate maternal clonalprogenies. Although apomixis in grasses is mainly expressed at the polyploid level, some natural diploid genotypesof Paspalum rufum produce aposporous embryo sacs in relatively high proportions and are even able tocomplete apomixis under specific conditions. However, despite the potential for apomixis, sexuality prevails indiploids, and apomixis expression is repressed for an as yet undetermind reason. Apomixis is thought to derivefrom a deregulation of one or a few components of the sexual pathway that could be triggered by polyploidy and/orhybridization. The objectives of this work were to characterize and compare the reproductive development and thetiming of apospory initial (AI) emergence between diploid genotypes with potential for apomixis and facultativeapomictic tetraploid cytotypes of P. rufum.Methods: Reproductive characterization was performed by cytoembryological observations of clearedovaries and anthers during all reproductive development steps and by quantitative evaluation of the ovule growthparameters.Key Results: Cytoembryological observations showed that in diploids, both female and male reproductivedevelopment is equally synchronized, but in tetraploids, megasporogenesis and early megagametogenesis aredelayed with respect to microsporogenesis and early microgametogenesis. This delay was also seen when ovarygrowth was taken as a reference parameter. The analysis of the onset of AIs revealed that they emerge during differentdevelopmental periods depending on the ploidy level. In diploids, the AIs appeared along with the tetrad (ortriad) of female meiocytes, but in tetraploids they appeared earlier, at the time of the megaspore mother cell. Inboth cytotypes, AIs can be seen even during megagametogenesis.Conclusions: Overall observations reveal that female sexual reproductive development is delayed in tetraploidsas compared with diploid genotypes, mainly at meiosis. In tetraploids, AIs appear at earlier sexual developmentalstages than in diploids, and they accumulate up to the end of megasporogenesis. The longer extension ofmegasporogenesis in tetraploids could favour AI emergence and also apomixis success.