A Robust Auxin Response Network Controls Embryo and Suspensor Development through a Basic Helix Loop Helix Transcriptional Module

Abstract

Land plants reproduce sexually by developing an embryo from a fertilized egg cell. However, embryos can also be formed from other cell types in many plant species. Thus, a key question is how embryo identity in plants is controlled, and how this process is modified during nonzygotic embryogenesis. The Arabidopsis (Arabidopsis thaliana) zygote divides to produce an embryonic lineage and an extra-embryonic suspensor. Yet, normally quiescent suspensor cells can develop a second embryo when the initial embryo is damaged, or when response to the signaling molecule auxin is locally blocked. Here we used auxindependent suspensor embryogenesis as a model to determine transcriptome changes during embryonic reprogramming. We found that reprogramming is complex and accompanied by large transcriptomic changes before anatomical changes. This analysis revealed a strong enrichment for genes encoding components of auxin homeostasis and response among misregulated genes. Strikingly, deregulation among multiple auxin-related gene families converged upon the reestablishment of cellular auxin levels or response. This finding points to a remarkable degree of feedback regulation to create resilience in the auxin response during embryo development. Starting from the transcriptome of auxin-deregulated embryos, we identified an auxin-dependent basic Helix Loop Helix transcription factor network that mediates the activity of this hormone in suppressing embryo development from the suspensor.

Current Perspectives on the Auxin-Mediated Genetic Network that Controls the Induction of Somatic Embryogenesis in Plants

“…Six of eleven YUC genes, YUC1, YUC2, YUC4, YUC6, YUC10 and YUC11, were found to be expressed in different embryogenic cultures of Arabidopsis [36,64,65]. It is worth noting that the SE-associated YUCs were specifically expressed in the shoot part of a plant and that most of them were active in ZE [66,67]. The expression of the SE-involved YUCs was localised in the SE-involved explant part, i.e., in the cotyledons of the immature zygotic embryo, and that the relevant single and multiple yuc mutants, including yuc2, yuc4 and yuc1, yuc4, yuc10 and yuc11 had a severely reduced capacity for SE [36,65,68].…”

Minimal auxin sensing levels in vegetative moss stem cells revealed by a ratiometric reporter

“…This R2D2 (ratiometric version of two D2s) system for rapid, sensitive and high-resolution detection of auxin sensing activities in living Arabidopsis tissues is now widely used (e.g. Caggiano et al, 2017;Di Mambro et al, 2017;Larsson et al, 2017;Liu et al, 2017;Bhatia et al, 2019;Feraru et al, 2019;Radoeva et al, 2019).…”

The short and intricate life of the suspensor

“…In a recent article, Radoeva et al () found large‐scale transcriptional changes in suspensors of an iaa12 gain‐of‐function mutant background using a suspensor‐specific driver. Mutation of IAA12 caused aberrant embryo‐like divisions in the suspensor (Rademacher et al ).…”