The xyloglucan endotransglucosylase/hydrolase TaXTH16 enhances wheat drought tolerance and pre-harvest sprouting resistance via ABA-mediated pathways.

INTRODUCTION Drought and PHS are major constraints on wheat production worldwide. Cell wall remodeling plays a crucial role in plant adaptation to water deficit. Xyloglucan endotransglucosylase/hydrolases (XTHs) are key cell wall-modifying enzymes, yet how they integrate with ABA signaling, the central pathway controlling drought responses and seed dormancy, remains unknown in wheat.

Objectives

The primary objective of this study is to functionally characterize TaXTH16 in drought tolerance and PHS resistance, with a focus on its transcriptional regulation by ABA responsive transcription factors and its natural haplotype variation for breeding applications.

Methods

We generated TaXTH16 overexpression and CRISPR/Cas9 knockout wheat lines for drought and PHS phenotyping. We performed biochemical assays for XET activity and subcellular localization, physiological measurements of water loss rate, stomatal aperture, ABA content, and ROS levels, transcriptomic analysis, and molecular assays including Y1H, EMSA, ChIP-qPCR, and dual-luciferase. Haplotype analyses were conducted across a wide range of wheat accessions.

Results

TaXTH16 encodes a functional XET enzyme localized to the plasma membrane and cell wall. Overexpression of TaXTH16 significantly enhanced drought tolerance, whereas knockout lines were more sensitive. TaXTH16 promoted xyloglucan and cellulose accumulation and enhanced ABA-mediated stomatal closure and ROS scavenging under drought. It also positively regulated PHS resistance, likely via ABA-mediated pathways. TaABF2 was identified as a direct transcriptional activator of TaXTH16. A natural variant, TaXTH16-2B-HapII, showed a higher promoter activity, significant association with greater drought resistance, and enrichment in modern cultivars.

Conclusion

This study establishes TaXTH16 as a positive regulator of wheat drought tolerance and PHS resistance, linking ABA signaling and cell wall remodeling. TaXTH16 is directly activated by TaABF2, and TaXTH16-2B-HapII represents a promising allele for breeding. These findings provide mechanistic insights into ABA-cell wall crosstalk and a valuable resource for improving wheat stress resilience.