AtGRP3 is a glycine-rich protein (GRP) from Arabidopsis thaliana shown to interact with the receptor-like kinase AtWAK1 in yeast, in vitro and in planta. In this work, phenotypic analyses using transgenic plants were performed in order to better characterize this GRP. Plants of two independent knockout alleles of AtGRP3 develop longer roots suggesting its involvement in root size determination. Confocal microscopy analysis showed an abnormal cell division and elongation in grp3-1 knockout mutants. Moreover, we also show that grp3-1 exhibits an enhanced Aluminum (Al) tolerance, a feature also described in AtWAK1 overexpressing plants. Together, these results implicate AtGRP3 function root size determination during development and in Al stress.

The presence of two meristematic cell populations in the root and shoot apex allow plants to grow indefinitely. Due to its simple and predictable tissue organisation, the Arabidopsis root apical meristem remains an ideal model to study mechanisms such as stem cell specification, asymmetric cell division and differentiation in plants. The root stem cell niche consists of a quiescent organizing center surrounded by mitotically active stem cells, that originate all root tissues. The transcription factors PLETHORA, SCARECROW and WOX5 form the signaling hubs that integrate multiple inputs from an increasing number of proteins implicated in the regulation of the stem cell niche function. Recently, locally produced auxin was added to the list of important mobile factors in stem cell niche. In addition, protein-protein interaction data elegantly demonstrated how parallel pathways can meet into a common objective. Here we discuss in a comprehensive way how multiple networks converge to specify and maintain the root stem cell niche.

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Plant development continues post-embryonically with a lifelong ability to form new tissues and organs. Asymmetric cell division, coupled with fate segregation, is essential to create cellular diversity during tissue and organ formation. Arabidopsis (Arabidopsis thaliana) plants harboring mutations in the SCHIZORIZA (SCZ) gene display fate segregation defects in their roots, resulting in the presence of an additional layer of endodermis, production of root hairs from sub-epidermal tissue, and misexpression of several tissue identity markers. Some of these defects are observed in tissues where SCZ is not expressed, indicating that part of the SCZ function is non-autonomous. As a class B HEAT-SHOCK TRANSCRIPTION FACTOR (HSFB), the SCZ protein contains several conserved domains and motifs. However, which domain(s) discriminates SCZ from its family members to obtain a role in development remains unknown. Here, we investigate how each domain contributes to SCZ function in Arabidopsis root patterning by generating altered versions of SCZ by domain swapping and mutation. We show that the SCZ DNA-Binding Domain is the main factor for its developmental function and that SCZ likely acts as a non-motile transcriptional repressor. Our results demonstrate how members of the HSF family can evolve toward functions beyond stress response.