Auxin and root initiation in somatic embryos of Arabidopsis

Abstract

Somatic embryos of Arabidopsis thaliana can be produced from explants of developing zygotic embryos. Cultivation of explants on maturation medium results in development of three main classes of regenerative structures: adventitious shoots, fused shoots, and complete somatic embryos. The ontogeny and anatomy of these structures was examined using serial plastic sections. Furthermore, two molecular markers were assayed to monitor transcriptional auxin responses and formation of a root meristem in this process: the LENNY allele of PIN4, a transposon insertion creating a fusion to the reporter gene GUS; and DR5::GUS, a synthetic reporter of auxin-induced transcription. In zygotic embryogenesis, PIN4 expression is confined to the center of the root meristem and begins to be detectable by the globular stage of embryogenesis, while DR5::GUS expression marks an "auxin perception maximum" in the more distal regions of the root. Adventitious and fused shoots develop no anatomically recognizable root meristem and do not express either of the two markers at their basal pole. Instead, the vasculature of their axis is directly connected to the vasculature of the explant. By contrast, complete somatic embryos were only loosely attached to the explant, had an anatomically defined root meristem and showed expression of both markers at their root pole. Our results suggest that the establishment of a root meristem in somatic embryos required appropriate auxin levels during the course of their development.

Is the auxin influx carrierLAX3essential for plant growth and development in the model plantsMedicago truncatula, Lotus japonicusandArabidopsis thaliana?

“…It is known that the combined action of auxin efflux carriers PIN1, PIN4 and PIN7 plays an essential role in auxin transport, cell division and auxin distribution during all stages of zygotic embryogenesis. [36,61,64,65] Since it is well known that auxin cell-to-cell transport is mediated by auxin influx (LAX proteins) and efflux (PIN proteins) carriers [40] and the plant hormone auxin plays an important role in every aspect of plant growth and development, including embryogenesis, [1,66] we confirmed the involvement of MtLAX3 in somatic embryo development.…”

“…E for 12À16 h. [61] Afterwards, the immature zygotic embryos were excised from the siliques under a microscope. To induce formation of embryogenic callus tissue formation, approximately 20 immature zygotic embryos were cultured on B5 solid medium supplemented with 0.9 mg/L 2.4D, and placed in dark for 14 days.…”

A transcriptional view on somatic embryogenesis

“…Bassuner, Lam, Lukowitz, and Yeung (2007) examined the histology of adventitious shoot and root formation during indirect SE from immature zygotic embryo explants. Single or fused shoots were connected to the explant by a broad tissue base, whereas somatic embryos developed from isolated cell clusters with only a weak connection to the explant.…”

Osmotic stress stimulates shoot organogenesis in callus of rice (Oryza sativa L.) via auxin signaling and carbohydrate metabolism regulation

“…In our previous studies, endogenous auxin, zeatin and ABA were at high levels in highly regenerable rice callus (Liu and Lee 1996;Huang et al 2012). Auxin might be the main factor controlling cell differentiation (Bassuner et al 2007;Petrásek and Friml 2009;Rademacher et al 2012). Our previous studies indicated that endogenous auxin levels in rice calli may play critical roles during shoot regeneration (Huang et al 2012).…”