Characterization of CRISPR-Cas9 Induced SAUR19 Family Mutants in Arabidopsis.

The plant hormone auxin (IAA) regulates many aspects of plant growth and development. Small auxin up RNA (SAUR) genes are highly transcribed in response to auxin, whose differential transport and accumulation creates gradients that regulate various aspects of plant development such as: tropisms, root initiation, and cellular division and differentiation. Previous studies using overexpression of GFP-tagged SAUR proteins have shown that SAURs may function as positive regulators of cellular expansion. To provide additional evidence for this hypothesis, I investigated the effect of creating knockouts of multiple members of the SAUR19 subfamily using CRISPR/Cas9. Additionally, SAUR-promoter-GUS staining was performed to identify the location of SAUR 13, 22, 27, 28, and 29 expression. These studies revealed strong SAUR expression in adult leaf vasculature, expanding stamen filaments, hypocotyls, and petioles. Through analysis of heat-induced growth, we show that knockout of SAURs 19, 20, 21, 22, 24, and 29 conferred a modest decrease in both hypocotyl and petiole length. While not severe, this difference provides supportive evidence that SAURs function as positive regulators of cell expansion, and it also reinforces the hypothesis that SAURs have extensive genetic redundancy. Higher numbers of SAUR knockouts should produce stronger phenotypes and provide definitive evidence of SAUR function.This research was supported by the Gray Laboratory

Network architecture and regulatory logic in neural crest development

The neural crest is an ectodermal cell population that gives rise to over 30 cell types during vertebrate embryogenesis. These stem cells are formed at the border of the developing central nervous system and undergo extensive migration before differentiating into components of multiple tissues and organs. Neural crest formation and differentiation is a multistep process, as these cells transition through sequential regulatory states before adopting their adult phenotype. Such changes are governed by a complex gene regulatory network (GRN) that integrates environmental and cell‐intrinsic inputs to regulate cell identity. Studies of neural crest cells in a variety of vertebrate models have elucidated the function and regulation of dozens of the molecular players that are part of this network. The neural crest GRN has served as a platform to explore the molecular control of multipotency, cell differentiation, and the evolution of vertebrates. In this review, we employ this genetic program as a stepping‐stone to explore the architecture and the regulatory principles of developmental GRNs. We also discuss how modern genomic approaches can further expand our understanding of genetic networks in this system and others