Improved gene editing technologies reveal how auxin controls Arabidopsis flower initiation

Abstract

Department of Cell and Developmental Biology, University of California San Diego, La Jolla, CA 92093-0116, USA

Auxin is known to be required for flower initiation. Mutations that disrupt either auxin biosynthesis, or auxin transport, or signaling result in the development of pin-like inflorescences. Among the pin-like mutants, pin-formed 1 (pin1), which encodes an auxin transporter, has been at the center of research in plant developmental biology. PIN1 activity and localization have been reported to be positively and directly regulated by PINOID (PID), a protein kinase, through phosphorylation. My group has developed several technologies that enable precise modifications of genes in plants. The technological advances provide unprecedented tools for us to study auxin biology. In this presentation, I will briefly describe the efficient gene targeting technology and in situ tagging genes with GFP and other tags using CRISPR-based homologous recombination. The technology avoids the pitfalls of transgenic approaches such as co-suppression and ectopic overexpression. We knocked GFP into PIN1 locus to generate in-frame PIN1-GFP fusion using our gene-editing technology. Surprisingly, the PIN1-GFPHDR fusion suppressed pid phenotypes, in a semi-dominant fashion. We further showed that pid mutants were suppressed when one copy of PIN1 gene is inactivated, while homozygous pin1 mutations enhanced pid phenotypes. Our observations are not compatible with the model that PIN1 is positively and directly regulated by PID. Moreover, we demonstrated that PID is not directly involved in PIN1 phosphorylation. In addition, we have shown that NPY1, which enhances pid phenotypes when mutated and which completely suppresses pid mutants when overexpressed. Interestingly, we discovered that overexpression of NPY1 increases phosphorylation of PIN1 and the phosphorylation actually inhibits PIN activities. Our latest results lead to a dramatic revision of previous models regarding the relationship between PIN1 and PID and overall auxin-mediated flower development.

Dr. Yunde Zhao is a Tata Chancellor’s Endowed Professor in the Department of Cell and Developmental Biology, University of California San Diego (UCSD). Dr. Zhao is the current Editor-in-Chief of Plant Physiology, which is one of the most prestigious plant biology journals.

Dr. Zhao is known for his contribution to solving the complete auxin biosynthetic pathway in plants. He played a leading role in demonstrating that local auxin biosynthesis is essential for plant development. Dr. Zhao is also recognized for his inventions of several gene editing-related technologies including ribozyme-based guide RNA production and the Transgene-Killer CRISPR technology, which have been widely used by scientists around the world. His recent invention of RUBY, a synthetic gene for betalain synthesis, greatly simplifies plant transformation and visualization of gene expression. A gallery of RUBY plants can be found here (https://zhaolab.biosci.ucsd.edu/ruby(link is external)). Dr. Zhao’s discoveries have been included in textbooks in three different fields: Plant Physiology and Development; Organic Chemistry; and Plant Biotechnology and Genetics.

Dr. Zhao received his Ph.D. in Biochemistry from the University of Michigan, where he studied nitric oxide signaling mechanisms in animals. Dr. Zhao received his postdoctoral training in the field of plant molecular genetics at the Salk Institute, where he was supported by a postdoctoral fellowship from the Howard Hughes Medical Institute and the Life Sciences Research Foundation. Dr. Zhao has been a Web of Science Highly Cited Researcher since 2019 and he has received several awards including ASPB Fellow, Fellow of Indian Society of Plant Physiology, the Japan Society for the Promotion of Science professor fellowship, and Fellow of AAAS.

https://scholar.google.com/citations?user=HnD2xxIAAAAJ&hl=en (link is external)

https://biology.ucsd.edu/research/faculty/y3zhao (link is external)