Chitinase-like1 Plays a Role in Stalk Tensile Strength in Maize

Abstract

Stalk lodging in maize (<i>Zea mays</i>) causes significant yield losses due to breaking of stalk tissue below the ear node before harvest. Here, we identified the maize <i>brittle stalk4</i> (<i>bk4</i>) mutant in a <i>Mutator</i> F2 population. This mutant was characterized by highly brittle aerial parts that broke easily from mechanical disturbance or in high-wind conditions. The <i>bk4</i> plants displayed a reduction in average stalk diameter and mechanical strength, dwarf stature, senescence at leaf tips, and semisterility of pollen. Histological studies demonstrated a reduction in lignin staining of cells in the <i>bk4</i> mutant leaves and stalk, and deformation of vascular bundles in the stalk resulting in the loss of xylem and phloem tissues. Biochemical characterization showed a significant reduction in <i>p</i>-coumaric acid, Glc, Man, and cellulose contents. The candidate gene responsible for <i>bk4</i> phenotype is <i>Chitinase-like1</i> protein (<i>Ctl1</i>), which is expressed at its highest levels in elongated internodes. Expression levels of secondary cell wall cellulose synthase genes (<i>CesA</i>) in the <i>bk4</i> single mutant, and phenotypic observations in double mutants combining <i>bk4</i> with <i>bk2</i> or null alleles for two <i>CesA</i> genes, confirmed interaction of <i>ZmCtl1</i> with <i>CesA</i> genes. Overexpression of <i>ZmCtl1</i> enhanced mechanical stalk strength without affecting plant stature, senescence, or fertility. Biochemical characterization of <i>ZmCtl1</i> overexpressing lines supported a role for ZmCtl1 in tensile strength enhancement. Conserved identity of CTL1 peptides across plant species and analysis of Arabidopsis (<i>Arabidopsis thaliana</i>) <i>ctl1-1 ctl2-1</i> double mutants indicated that <i>Ctl1</i> might have a conserved role in plants.