Nuter, M. | Search bioRxiv

bioRxiv2026

Control of grain dimensions via ALLENE OXIDE CYCLASE

Cereal grain is a global food staple. Grain formation starts with fertilization of the embryo sac which generates filial tissues, such as the embryo and endosperm, that grow embedded in the maternal ovule and surrounding ovary wall. Maternal tissues provide nutrition and protection but are progressively reduced and degraded, such that filial tissues dominate the mature grain. While we know some enzymatic players, regulation of this process in temperate cereals like wheat and barley, remains less understood. However, previous work suggested a role for the phytohormone Jasmonate (JA). To learn more, we edited the barley ALLENE OXIDASE CYCLASE (HvAOC) gene encoding a JA biosynthetic enzyme. Defective HvAOC alleles caused enhanced vegetative growth, faster flowering and larger, heavier grain - phenotypes rescued by MeJA treatment. HvAOC control of final grain parameters is parentally-derived, consistent with enriched HvAOC expression in maternal compared to filial tissues. Defective HvAOC function enlarged maternal tissues involved in nutrient transfer, correlating with larger endosperm and higher expression of genes linked to sucrose transport. This work provides the first genetic dissection of JA in barley and highlights a key role for HvAOC in the coordination between growth and death of maternal tissues with grain size and weight.

plant biology↗

bioRxiv2025

Barley BODYGUARD controls cuticular specialisations regulated by SHINE transcription factors

The outer epidermis of land plants secretes a cuticular layer, a hydrophobic diffusion barrier which minimises water loss into the atmosphere and protects from pests, ultraviolet light and organ fusion. Cuticles typically comprise a polyester cutin matrix embedded and overlaid with cuticular waxes, but their exact chemical make-up, structure and functions can vary widely depending on the tissue and species. Barley shows two such cuticular specialisations: (1) deposition of a thick {beta}-diketone-rich wax bloom on multiple organs at reproductive stage, common in other Poeceae species and linked to yield; and, (2) secretion of a sticky layer on the grain fruit (caryopsis) pericarp cuticle which adheres to inner floral hulls, leading to barleys distinctive covered grain used in animal feed and malting. Two SHINE/WAX-INDUCER transcription factors in barley, HvWIN1 and NUD, promote the wax bloom and hull to caryopsis adhesion, respectively, yet little is understood about other genes involved. Leveraging near-isogenic lines of wax-deficient mutants, we identify the barley BODYGUARD1 (HvBDG1) gene encoding an /{beta}-hydrolase essential for leaf cuticular integrity and wax bloom deposition. Modelling of functional and defective alleles suggests that HvBDG1 N-terminal region control of protein flexibility is important for HvBDG1 function. In addition to their role in controlling barley epicuticular wax deposition, we show that both HvBDG1 and HvWIN1 are essential for strong hull to caryopsis adhesion. Along with NUD, these gene products differentially contribute to ultrastructural changes on the pericarp associated with a cuticular building programme driven by NUD and HvWIN1 regulation of cuticle metabolism and transport and cell wall-related genes, and correlate with shifts in pericarp surface chemistry. We also show that the previously asserted grain-specific role of NUD should be revised, as our findings reveal that it is essential for maintaining leaf cuticle integrity. Our analyses in barley suggest that NUD and HvWIN1 control cuticular specialisations and cuticle integrity in part via promotion of HvBDG1 expression, while HvWIN1 and NUD likely act independently from each other. Lastly, mining tetraploid wheat mutant populations followed by crossing to combine mutated homoeologues demonstrated that BDG1 and WIN1 orthologues also control wax bloom in wheat. Taken together, our work greatly expands the genetic networks and molecular activities important for cuticle development in cereals and the underlying mechanisms for both shared and species-specific cuticular specialisations.

plant biology↗