Validation and expression analysis of candidate genes for adventitious rooting, in micro-cuttings of Acca sellowiana (Myrtaceae)

Acca sellowiana (Myrtaceae) is a multipurpose species with edible fruits and ornamental value, native to Uruguay and southern Brazil. Domestication of the species in Uruguay is incipient although in other countries, it is widely cultivated. It is an evergreen out-crossing shrub, pollinated by birds and bees. For this reason, it is necessary to develop vegetative propagation strategies such as stem cuttings to reproduce outstanding genotypes for conservation or breeding programs. Adventitious root (AR) formation in cuttings is regulated by environmental and endogenous factors. Among phytohormones, indole-butyric acid (IBA) is the most widely exogenous auxin used to improve rooting of cuttings. Most studies on AR formation at the molecular level use model species; however, the conservation of these mechanisms in non-model plants has been little studied, consequently the effects of different factors and their interactions in A. sellowiana are not well understood. The identification and expression analysis of genes known to be involved in the regulation of the process is an important step to elucidate the molecular mechanisms that regulate AR differentiation in A. sellowiana cuttings. In this study, we compared two genotypes with contrasting rooting ability, and we identified and characterized three genes that might regulate the onset of AR development in A. sellowiana: AsPIN1, AsTIR1 and AsSHR. Their expression analysis showed that in the difficult-to-root genotype, AsTIR1 increases strongly in response to exogenous IBA, shortly after induction treatment. Relative expression of AsPIN1 and AsSHR also increases 24 h later. The biological significance of this gene expression pattern is discussed.