Maize WI5 encodes an endo-1,4-β-xylanase required for secondary cell wall synthesis and water transport in xylem.

Water transport from roots to leaves through xylem is important for plant growth and development. Defects in water transport can cause drought stress, even when there is adequate water in the soil. Here, we identified the maize (Zea mays) wilty5 (wi5) mutant, which exhibits marked dwarfing and leaf wilting throughout most of its life cycle under normal growth conditions. wi5 seedlings exhibited lower xylem conductivity and wilted more rapidly under drought, NaCl, and high temperature treatments than wild type plants. Map-based cloning revealed that WI5 encodes an active endo-1,4-β-xylanase from glycosyl dehydration family 10, which mainly functions in degrading and reorganizing cell wall xylan. RT-PCR and GUS assays revealed that WI5 is highly expressed in stems, especially in internodes undergoing secondary wall assembly. RNA-seq suggested that WI5 plays a unique role in internode growth. Immunohistochemistry and electron microscopy confirmed that wi5 is defective in xylan deposition and secondary cell wall thickening. Lignin deposition and xylan content were markedly reduced in wi5 compared to the wild type plants. Our results suggest that WI5 functions in xylem cell wall thickening through its xylanase activity and thereby regulates xylem water transport, the drought stress response, and plant growth in maize. This article is protected by copyright. All rights reserved.