Rhizogenesis on in-vitro plantlets of Caricapapayal.: identification and expression profiling of transcription repressors of response to auxin (Aux/IAA) and auxin response factor (ARF) genes

摘要

Mexico is currently the leading exporter of papaya [Carica papaya L.) worldwide, in particular of 'Maradol'. The economic importance of this activity has created the need to establish biotechnological strategies to mass-micropropagate this species. However, papaya has proved to be a "difficult-to-root" species. The low rooting percentages, which eventually lead to high mortality when transferring to ex-vitro conditions, have presented serious difficulties for propagating this species. The auxin indoIe-3-butyric acid (IBA) has often been used in culture media to achieve adventitious root formation in papaya in-vitro plantlets. This root stimulation is a consequence of auxin regulation by transcription factors (TFs) of the ARF (auxin response factors)and Aux/IAA (transcription repressors of response to auxin) types. These TFs activate or repress lateral root formation processes. The objective of the present work was to understand the molecular mechanisms of rhizogenesis through expression profilinganalysis of genes involved in the inhibition (CpAux/IAA12, CpAux/IAA13 and CpAux/IAA14) or activation (CpARF5, CpARF6 and CpARF7) of rhizogenesis on in-vitro plantlets of C. papaya L. 'Maradol' exposed to different rhizogenesis-inducing systems. In-vitroplantlets exposed to exogenous IBA in the culture medium were able to form roots, and consequently had high ex-vitro survival rates (83%). In general, these in-vitro plantlets presented low expression of CpAux/IAA repressor genes in both stem-base and root tissues, but high expression of CpARF genes, which are auxin activator genes. Interestingly, the opposite occurred in treatments where the in-vitro plantlets were unable to produce roots.