ZmSRL5 is involved in drought tolerance by maintaining cuticular wax structure in maize

Cuticular wax is a natural barrier on terrestrial plant organs, which protects plants from damages caused by a variety of stresses. Here, we report the identification and functional characterization of a cuticular-wax-related gene, Zea mays L. SEMI-ROLLED LEAF 5 (ZmSRL5). The loss-of-function mutant srl5, which was created by a 3,745 bp insertion in the first intron that led to the premature transcript, exhibited abnormal wax crystal morphology and distribution, which, in turn, caused the pleiotropic phenotypes including increased chlorophyll leaching and water loss rate, decreased leaf temperature, sensitivity to drought, as well as semi-rolled mature leaves. However, total wax amounts showed no significant difference between wild type and semi-rolled leaf5 (srl5) mutant. The phenotype of srl5 was confirmed through the generation of two allelic mutants using CRISPR/Cas9. ZmSRL5 encodes a CASPARIAN-STRIP-MEMBRANE-DOMAIN-LIKE (CASPL) protein located in plasma membrane, and highly expressed in developing leaves. Further analysis showed that the expressions of the most wax related genes were not affected or slightly altered in srl5. This study, thus, primarily uncovers that ZmSRL5 is required for the structure formation of the cuticular wax and could increase the drought tolerance by maintaining the proper cuticular wax structure in maize.