Dynamics of Endogenous Auxin and Its Role in Somatic Embryogenesis Induction and Progression in Cork Oak

Abstract

Somatic embryogenesis (SE) is a feasible in vitro regeneration system with biotechnological applications in breeding programs, although, in many forest species, SE is highly inefficient, mainly due to their recalcitrance. On the other hand, SE represents a valuable model system for studies on cell reprogramming, totipotency acquisition, and embryogenic development. The molecular mechanisms that govern the transition of plant somatic cells to embryogenic cells are largely unknown. There is increasing evidence that auxins mediate this transition and play a key role in somatic embryo development, although data on woody species are very limited. In this study, we analyzed the dynamics and possible role of endogenous auxin during SE in cork oak (Quercus suber L.). The auxin content was low in somatic cells before cell reprogramming, while it increased after induction of embryogenesis, as revealed by immunofluorescence assays. Cellular accumulation of endogenous auxin was also detected at the later stages of somatic embryo development. These changes in auxin levels correlated with the expression patterns of the auxin biosynthesis (QsTAR2) and signaling (QsARF5) genes, which were upregulated after SE induction. Treatments with the inhibitor of auxin biosynthesis, kynurenine, reduced the proliferation of proembryogenic masses and impaired further embryo development. QsTAR2 and QsARF5 were downregulated after kynurenine treatment. Our findings indicate a key role of endogenous auxin biosynthesis and signaling in SE induction and multiplication, as well as somatic embryo development of cork oak.

DNA demethylation by transitory 5‐azacytidine treatment improves somatic embryogenesis yield for regeneration and breeding of cork oak

“…It is suggested microRNAs and epigenetic factors, such as DNA methylation, histone modifications and chromatin remodeling, could modulate auxin biosynthesis, transport, and signal transduction (Maury et al 2019). In this context, endogenous auxin accumulation takes place in developing somatic embryos in cork oak, which is related to the expression profiles of the auxin biosynthesis gene QsTAR2 and the signaling gene QsARF5 (Carneros et al 2023). These results are in consonance with the hypermethylation of DNA reported in the present study at advanced stages of somatic embryo development in cotyledonary embryos.…”

Opposite Auxin Dynamics Determine the Gametophytic and Embryogenic Fates of the Microspore

“…This hormone plays a crucial role in both direct embryogenesis processes, to initiate embryo development, and indirect embryogenesis, for the formation of proembryogenic masses and the subsequent development of somatic embryos. However, the mechanisms that regulate the triggering of these processes in the presence of auxin remain largely unknown [ 2 , 16 , 48 , 61 ]. In various species where indirect embryogenesis is induced, high levels of auxin have been observed during the proliferation of proembryogenic masses and early somatic embryo development [ 41 , 62 , 63 , 64 , 65 ].…”

“…Our results have revealed a high concentration of auxin in proembryos during the early embryogenic divisions, suggesting a role for this hormone in the activation of either cell reprogramming and/or proliferation that follows immediately. Studies conducted on the somatic embryogenesis of other species have shown an increase in endogenous IAA levels throughout the process [ 17 , 57 , 61 , 67 , 68 , 69 , 70 , 71 ], indicating the activation of de novo auxin biosynthesis, polar transport, and signaling pathways, evidenced by high expression levels of the biosynthesis genes YUC , TAA1 , and TAR2 ; the auxin polar transport gene PIN1 ; and the signaling genes Aux / IAA and ARF . In Arabidopsis zygotic embryogenesis, an increase in auxin levels was observed in ovule tissues after fertilization [ 72 ], as well as in zygotic embryo cells from the very beginning of their formation [ 18 , 73 ].…”