[CEPCEB_All] CEPCEB Seminar: Aman Husbands 2/6/26

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*Aman Husbands*
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*“Out of one, many”: paralog-specific regulons from a single network
architecture*


*Date:* Friday, February 6

*Time:* 12:00 pm-1:00pm

*Location: *Genomics Auditorium 1102


*Abstract:*

Functional divergence of transcription factors (TFs) has driven cellular
and organismal complexity throughout evolution, but its mechanistic drivers
remain poorly understood. The CLASS III HOMEODOMAIN LEUCINE ZIPPER
(HD-ZIPIII) TFs are an ideal model to address this knowledge gap. HD-ZIPIII
TFs arose over 725 million years ago and proliferated over the course of
evolution. In the model plant *Arabidopsis thaliana,* there are five
HD-ZIPIII paralogs that impact nearly all aspects of development through
functionally redundant and divergent activities. We recently identified a
regulatory mechanism driving HD-ZIPIII TF functional divergence*.*
Specifically,
we found that two co-expressed, functionally divergent HD-ZIPIII family
members – *CORONA (CNA)* and *PHABULOSA (PHB) – *bind a nearly overlapping
set of genes. Despite this, CNA and PHB have hundreds of uniquely regulated
direct targets. Regulation of a given gene by CNA or PHB is thus a function
of whether a bound site is considered ‘responsive’ versus ‘non-responsive’
by each paralog. Discrimination between responsive and non-responsive sites
is controlled, at least in part, by their lipid binding START domain. This
suggests a model in which HD-ZIPIII TFs use information integrated by their
START domain to generate paralog-specific transcriptional outcomes from a
shared network architecture. Taken together, we identify a mechanism of
HD-ZIPIII TF paralog divergence and propose the ubiquitously distributed
START evolutionary module as a driver of functional divergence.
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