
Short heat shock factors S-HsfA2, S-HsfA4c, and S-HsfB1 represent new types of heat shock factors that bind to a novel heat-regulated element and negatively regulate extreme heat tolerance in Arabidopsis to maintain proper plant growth.


coremsg

Cells prevent heat damage through a highly conserved canonical heat stress response (HSR) in which heat shock factors (HSFs) bind heat shock elements (HSEs) to activate heat shock proteins (HSPs). Plants generate short HSFs that originate from HSF splicing variants, but little is known about S-HSFs. Although an enhanced canonical HSR confers thermotolerance, its hyperactivation inhibits plant growth. How this process is prevented to ensure proper plant growth has not been determined. Here, we report that Arabidopsis S-HsfA2, S-HsfA4c, and S-HsfB1 confer extreme heat (45°C) sensitivity and represent new kinds of HSF with a unique truncated DNA-binding domain (tDBD) that binds a new heat-regulated element (HRE). The HRE conferred a minimal promoter response to heat and exhibited heat stress sensing and transmission patterns. We used S-HsfA2 to investigate whether and how S-HSFs prevent hyperactivation of the canonical HSR. HSP17.6B, a direct target gene of HsfA2, conferred thermotolerance, but its overexpression caused HSR hyperactivation. We revealed that S-HsfA2 alleviated this hyperactivation in two different ways. 1) S-HsfA2 negatively regulates HSP17.6B via the HRE-HRE-like element, thus constructing a noncanonical HSR (S-HsfA2-HRE- HSP17.6B ) to antagonistically repress HsfA2-activated HSP17.6B expression. 2) S-HsfA2 binds to the DBD of HsfA2 to prevent HsfA2 from binding to HSEs, eventually attenuating HsfA2-activated HSP17.6B promoter activity. Overall, our findings underscore the biological importance of S-HSFs, namely, preventing plant heat tolerance hyperactivation to maintain proper growth.

![Figure][1]</img>

### Competing Interest Statement

The authors have declared no competing interest.

 [1]: pending:yes

Short heat shock factor A2 confers heat sensitivity in Arabidopsis: Insights into heat resistance and growth balance

short-heat-shock-factor-a2-confers-extreme-heat-sensitivity-in-arabidopsis-insights-into-balancing-heat-resistance-and-plant-growth


Short Heat Shock Factor A2 Confers Extreme Heat Sensitivity in Arabidopsis: Insights into Balancing Heat Resistance and Plant Growth
