Hailiang Mao

Grain yield in many cereal crops is largely determined by grain size. Here we report the genetic and molecular characterization of GS3, a major quantitative trait locus for grain size. It functions as a negative regulator of grain size and organ size. The wild-type isoform is composed of four putative domains: a plant-specific organ size regulation (OSR) domain in the N terminus, a transmembrane domain, a tumor necrosis factor receptor/nerve growth factor receptor (TNFR/NGFR) family cysteine-rich domain, and a von Willebrand factor type C (VWFC) in the C terminus. These domains function differentially in grain size regulation. The OSR domain is both necessary and sufficient for functioning as a negative regulator. The wild-type allele corresponds to medium grain. Loss of function of OSR results in long grain. The C-terminal TNFR/NGFR and VWFC domains show an inhibitory effect on the OSR function; loss-of-function mutations of these domains produced very short grain. This study linked the functional domains of the GS3 protein to natural variation of grain size in rice.

Leaf rust, caused by Puccinia triticina Eriksson (Pt), is one of the most severe foliar diseases of wheat. Breeding for leaf rust resistance is a practical and sustainable method to control this devastating disease. Here, we report the identification of Lr47, a broadly effective leaf rust resistance gene introgressed into wheat from Aegilops speltoides. Lr47 encodes a coiled-coil nucleotide-binding leucine-rich repeat protein that is both necessary and sufficient to confer Pt resistance, as demonstrated by loss-of-function mutations and transgenic complementation. Lr47 introgression lines with no or reduced linkage drag are generated using the Pairing homoeologous1 mutation, and a diagnostic molecular marker for Lr47 is developed. The coiled-coil domain of the Lr47 protein is unable to induce cell death, nor does it have self-protein interaction. The cloning of Lr47 expands the number of leaf rust resistance genes that can be incorporated into multigene transgenic cassettes to control this devastating disease.

The widely recognized pleiotropic adult plant resistance gene Lr34 encodes an ATP-binding cassette transporter and plays an important role in breeding wheat for enhanced resistance to multiple fungal diseases. Despite its significance, the mechanisms underlying Lr34-mediated pathogen defense remain largely unknown. Our study demonstrates that wheat lines carrying the Lr34res allele exhibit thicker cell walls and enhanced resistance to fungal penetration compared to those without Lr34res. Transcriptome and metabolite profiling revealed that the lignin biosynthetic pathway is suppressed in lr34 mutants, indicating a disruption in cell wall lignification. Additionally, we discovered that lr34 mutant lines are hypersensitive to sinapyl alcohol, a major monolignol crucial for cell wall lignification. Yeast accumulation and efflux assays confirmed that the LR34 protein functions as a sinapyl alcohol transporter. Both genetic and virus-induced gene silencing experiments demonstrated that the disease resistance conferred by Lr34 can be enhanced by incorporating the TaCOMT-3B gene, which is responsible for the biosynthesis of sinapyl alcohol. Collectively, our findings provide novel insights into the role of Lr34 in disease resistance through mediating sinapyl alcohol transport and cell wall deposition, and highlight the synergistic effect of TaCOMT-3B and Lr34 against multiple fungal pathogens by mediating cell wall lignification in adult wheat plants.