PhD Exit Seminar – Sonhita Chakraborty (Yoshioka Lab)

Investigation of the biological function of plant Cyclic Nucleotide Gated Ion Channel 2 in auxin signaling

Abstract

Calcium (Ca²⁺) is a ubiquitously important signaling molecule in eukaryotic cells. For plants, developmental cues, and signals from the environment lead to changes in cellular Ca²⁺ concentrations that are required to activate appropriate responses. CYCLIC NUCLEOTIDE GATED CHANNELS (CNGCs) are ion channels that are thought to conduct cations like Ca²⁺ in plant cells. Of the 20 members of the Arabidopsis CNGC family, the isomer CNGC2 is of special interest as the loss-of-function of CNGC2 leads to defects in multiple physiological processes.

In this thesis, I investigated the biological function of CNGC2 and propose that CNGC2 is important in auxin homeostasis in addition to its prescribed role in immunity.

The first suppressor of the autoimmune CNGC2 null mutant was found to carry a mutation in the auxin biosynthesis gene YUCCA6 (YUC6). An investigation into alterations in auxin signals revealed that the CNGC2 knockout mutant dnd1/cngc2 exhibits abnormalities in auxin signaling and hyper-accumulates endogenous auxin, indole-3-acetic acid (IAA). This is the first report of CNGC2 being potentially involved in auxin signals through auxin biosynthesis. I next showed that a loss-of-function of another IAA biosynthesis gene, TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 (TAA1) also suppresses phenotypes associated with cngc2. This indicated that hyper-accumulation of IAA is a source of cngc2 phenotypes. IAA-induced Ca²⁺ influx is impaired in cngc2, and this phenotype is alleviated in the absence of YUC6. This indicates that CNGC2 functions in auxin-induced Ca²⁺ signals that can influence auxin homeostasis. The hyper accumulation of auxin in cngc2 positions CNGC2 in a negative feedback loop of auxin biosynthesis.

Since all 11 members of the YUC gene family are thought to be involved in auxin biosynthesis, I asked whether a loss-of-function in any YUC gene could suppress cngc2 phenotype. Of all the yuc mutants tested, only yuc6 could suppress cngc2 phenotypes. YUC6 and TAA1 have been shown to exhibit similar tissue-specific expression patterns at the vasculature, a pattern not observed with other YUCs. This indicates a specific role of YUC6 in the CNGC2-mediated auxin feedback loop, which may be governed by its unique expression pattern.

Collectively, these findings cast a new light of CNGC2’s complex regulation by auxin signaling and immune responses.

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Join Zoom Meeting

https://utoronto.zoom.us/j/81354513761

Meeting ID: 813 5451 3761

Host: Keiko Yoshioka (keiko.yoshioka@utoronto.ca)

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