Because plant mechanical strength influences plant growth and development, the regulatory mechanisms underlying cell-wall synthesis deserve investigation. Rice mutants are useful for such research. We have identified a novel brittle culm 25 (bc25) mutant with reduced growth and partial sterility. BC25 encodes an UDP-glucuronic acid decarboxylase involved in cellulose synthesis and belongs to the UXS family. A single-nucleotide mutation in BC25 accounts for its altered cell morphology and cell-wall composition. Transmission electron microscopy analysis showed that the thickness of the secondary cell wall was reduced in bc25. Monosaccharide analysis revealed significant increases in content of rhamnose and arabinose but not of other monosaccharides, indicating that BC25 was involved in xylose synthesis with some level of functional redundancy. Enzymatic assays suggested that BC25 functions with high activity to interconvert UDP-glucuronic acid (UDP-GlcA) and UDP-xylose. GUS staining showed that BC25 was ubiquitously expressed with higher expression in culm, root and sheath, in agreement with that shown by quantitative real-time (qRT)-PCR. RNA-seq further suggested that BC25 is involved in sugar metabolism. We conclude that BC25 strongly influences rice cell wall formation.

The development of rice cultivars with improved nitrogen use efficiency (NUE) is desirable for sustainable agriculture. Achieving this goal depends in part on understanding how rice responds to low soil nitrogen (N) and identifying causative genes underlying this trait. To identify quantitative trait loci (QTL) or genes associated with low N response, we conducted a genome-wide association study (GWAS) using a diverse panel of 230 rice accessions and performed a transcriptomic investigation of rice accessions with differential responses to low N stress at two N levels. We detected 411 GWAS-associated genes in 5 QTL and 2722 differentially expressed genes in response to low N, of which 24 were identified by both methods and ranked according to gene annotations, literature queries, gene expression, and genetic diversity analysis. The large-scale datasets obtained from this study reveal low N-responsive characteristics and provide insights towards understanding the regulatory mechanisms of N-deficiency tolerance in rice, and the candidate genes or QTL would be valuable resources for increasing rice NUE via molecular biotechnology.