Trick or Treat: TINY’s Trick on Plant Growth

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Zhouli Xie et al. demonstrate that TINY manipulates plant growth by inhibiting the brassinosteroid signaling pathway. The Plant Cell https://doi.org/10.1105/tpc.18.00918

By Zhouli Xie Trevor Nolan and Yanhai Yin

Background: Environmental challenges such as water deficit and extreme temperatures are associated with decreased plant growth and severe crop losses. Transcriptional regulatory mechanisms help plants cope with these unfavorable conditions. Among these, the AP2/ERF family transcription factors are key regulators of drought responses. Moreover, in many cases, AP2/ERF family transcription factors including TINY have an inhibitory effect on plant growth.

Question: We wanted to know how TINY inhibits plant growth and contributes to plant drought tolerance. Brassinosteroids (BRs) are polyhydroxylated plant steroid hormones that play important roles in plant growth, development and stress responses. Therefore, we tested TINY’s role in BR-mediated plant growth and drought responses in Arabidopsis.

Findings: We found that TINY highjacks the BR signaling pathway during drought stress to positively regulate drought tolerance and negatively regulate plant growth. However, to prevent activation of stress responses under optimal growth conditions, the BR pathway promotes TINY degradation by a negative regulator in the BR pathway, BIN2 kinase. BIN2 phosphorylates and stabilizes TINY during stress. Overexpression of TINY led to increased sensitivity to the BR biosynthesis inhibitor Brassinazole (BRZ) and compromised BR-responsive gene expression. TINY interacted with and inhibited BES1, a key positive BR signaling component in the regulation of these genes.

Next steps: Scientists aim to alter crop plants to increase stress tolerance while maintaining crop yield. Our work demonstrates how TINY, a positive regulator of stress, inhibits BR-regulated plant growth. However, the contribution of TINY to drought tolerance and the degradation of TINY under normal growth conditions might enable crop scientists to use this step-wise regulation to overcome growth-stress tradeoffs.

Zhouli Xie, Trevor Nolan, Hao Jiang, Buyun Tang, Mingcai Zhang, Zhaohu Li, & Yanhai Yin (2019) The AP2/ERF Transcription Factor TINY Modulates Brassinosteroid-Regulated Plant Growth and Drought Responses in Arabidopsis. https://doi.org/10.1105/tpc.18.00918

Figure caption: TINY overexpression lines are sensitive to BR biosynthesis inhibitor BRZ.

Key words: drought tolerance, brassinosteroid, Arabidopsis