Regulation of intercellular TARGET OF MONOPTEROS 7 protein transport in the Arabidopsis root

Abstract

Intercellular communication coordinates hypophysis establishment in the embryo. Previously, TARGET OF MONOPTEROS 7 (TMO7) was reported to be transported to the hypophysis, the founder cell of the root cap, and RNA suppression experiments implicated its function in embryonic root development. However, the protein properties and mechanisms mediating TMO7 protein transport, and the role the movement plays in development remained unclear. Here, we report that in the post-embryonic root, TMO7 and its close relatives are transported into the root cap through plasmodesmata in a sequence-dependent manner. We also show that nuclear residence is crucial for TMO7 transport, and postulate that modification, potentially phosphorylation, labels TMO7 for transport. Additionally, three novel CRISPR/Cas9-induced alleles confirmed a role in hypophysis division, but suggest complex redundancies with close relatives in root formation. Finally, we demonstrate that TMO7 transport is biologically meaningful, as local expression partially restores hypophysis division in a plasmodesmal protein transport mutant. Our study identifies motifs and amino acids that are pivotal for TMO7 protein transport, and establishes the importance of TMO7 in hypophysis and root development.

A Dual sgRNA Approach for Functional Genomics inArabidopsis thaliana

“…CRISPR/Cas9 technology has been established for Arabidopsis and is continuously being developed further ( Feng et al 2013 , Mao et al 2013 , Fauser et al 2014 , Feng et al 2014 , Ma et al 2015 , Wang et al 2015 , Osakabe et al 2016 , Tsutsui and Higashiyama 2017 , Zhang et al , 2016 , Denbow et al 2017 , Peterson et al 2016 ). Reports using CRISPR/Cas9 in Arabidopsis are emerging that are not technology-focused, but rather limited in number taking into account the widespread use of this model organism, the short generation time and its ease of transformation ( Gao et al 2015 , Ning et al 2015 , Xin et al 2016 , Zhang et al 2016 , Guseman et al 2017 , Li et al 2017 , Lu et al 2018 , Ritter et al 2017 , Durr et al 2018 ). The difficulties of using CRISPR/Cas9 to generate mutants in Arabidopsis have been attributed to the unique floral dip system of transformation in which inflorescences of T0 plants are infected with Agrobacterium tumefaciens .…”

Aiming for the top: non-cell autonomous control of shoot stem cells in Arabidopsis

“…Subsequent studies revealed that SRH movement is mediated by the endosome associated SHORT-ROOT INTERACT-ING EMBRYONIC LETHAL (SIEL), which also interacts with several other root specific transcription factors such as CAPRICE (CPC) and TARGET OF MONOPTEROUS 7 (TMO7) (Koizumi et al 2011). Additionally, nuclear localisation had been found to be crucial for both proteins (Kurata et al 2005;Lu et al 2018) and the addition of a strong NLS, but also of a nuclear export signal (NES) could disturb TMO7 mobility. Furthermore, TMO7 movement occurred unidirectionally towards the root tip and, similar to WUS, in a sequence specific manner, despite the small size of the protein (~ 11 kDa) that would certainly allow passive diffusion through plasmodesmata (Lu et al 2018).…”

“…Additionally, nuclear localisation had been found to be crucial for both proteins (Kurata et al 2005;Lu et al 2018) and the addition of a strong NLS, but also of a nuclear export signal (NES) could disturb TMO7 mobility. Furthermore, TMO7 movement occurred unidirectionally towards the root tip and, similar to WUS, in a sequence specific manner, despite the small size of the protein (~ 11 kDa) that would certainly allow passive diffusion through plasmodesmata (Lu et al 2018).…”

Photoinducible DRONPA‐s: a new tool for investigating cell–cell connectivity

“…Cell‐to‐cell movement of proteins and regulatory RNAs is essential for establishing cellular identity in meristematic tissues (Otero et al ., ). Transgenic Arabidopsis lines with blocked plasmodesmata in the globular embryo or in the endodermis of the root meristem developed severe defects in tissue patterning (Vatén et al ., ; Lu et al ., ). Generally, cells of undifferentiated tissues contain large and unbranched plasmodesmata that allow the exchange of signalling molecules involved in cell differentiation processes (Zhu et al ., ,b; Oparka et al ., ; Burch‐Smith and Zambryski, ).…”