Decoupling tillering and fertilization: For rice as an agricultural crop, more tillers, or branches that carry grains, are desired, as is less demand for nitrogen fertilization. Unfortunately, for many rice varieties, the number of tillers depends on the amount of nitrogen fertilization. Wu et al. now show that nitrogen status affects chromatin function through modification of histones, a process in which the transcription factor NGR5 recruits polycomb repressive complex 2 to target genes. Some of these genes regulate tillering, such that with more nitrogen, the plants develop more tillers. NGR5 is regulated by proteasomal destruction and mediates hormone signaling. An increase in NGR5 levels can drive increases in rice tillering and yield without requiring increases in nitrogen-rich fertilizer. Science , this issue p. eaaz2046

Improving the performance of rice (Oryza sativa) under drought stress has the potential to significantly affect rice productivity. Here, we report that the ERF family transcription factor OsLG3 positively regulates drought tolerance in rice. In our previous work, we found that OsLG3 has a positive effect on rice grain length without affecting grain quality. In this study, we found that OsLG3 was more strongly expressed in upland rice than in lowland rice under drought stress conditions. By performing candidate gene association analysis, we found that natural variation in the promoter of OsLG3 is associated with tolerance to osmotic stress in germinating rice seeds. Overexpression of OsLG3 significantly improved the tolerance of rice plants to simulated drought, whereas suppression of OsLG3 resulted in greater susceptibility. Phylogenetic analysis indicated that the tolerant allele of OsLG3 may improve drought tolerance in cultivated japonica rice. Introgression lines and complementation transgenic lines containing the elite allele of OsLG3^IRAT109 showed increased drought tolerance, demonstrating that natural variation in OsLG3 contributes to drought tolerance in rice. Further investigation suggested that OsLG3 plays a positive role in drought stress tolerance in rice by inducing reactive oxygen species scavenging. Collectively, our findings reveal that natural variation in OsLG3 contributes to rice drought tolerance and that the elite allele of OsLG3 is a promising genetic resource for the development of drought-tolerant rice varieties.

Summary: Grain size, one of the important components determining grain yield in rice, is controlled by the multiple quantitative trait loci (QTLs). Intensive artificial selection for grain size during domestication is evidenced in modern cultivars compared to their wild relatives. Here, we report the molecular cloning and characterization of OsLG3b, a QTL for grain length in tropical japonica rice that encodes MADS‐box transcription factor 1 (OsMADS1). Six SNPs in the OsLG3b region led to alternative splicing, which were associated with grain length in an association analysis of candidate region. Quantitative PCR analysis indicated that OsLG3b expression was higher during the panicle and seed development stages. Analysis of haplotypes and introgression regions revealed that the long‐grain allele of OsLG3b might have arisen after domestication of tropical japonica and spread to subspecies indica or temperate japonica by natural crossing and artificial selection. OsLG3b is therefore a target of human selection for adaptation to tropical regions during domestication and/or improvement of rice. Phylogenetic analysis and pedigree records showed that OsLG3b had been employed by breeders, but the gene still has much breeding potential for increasing grain length in indica. These findings will not only aid efforts to elucidate the molecular basis of grain development and domestication, but also facilitate the genetic improvement of rice yield.

Most agronomic traits in rice are complex and polygenic. The identification of quantitative trait loci (QTL) for grain length is an important objective of rice genetic research and breeding programs. Herein, we identified 99 QTL for grain length by GWAS based on approximately 10 million single nucleotide polymorphisms from 504 cultivated rice accessions (Oryza sativa L.), 13 of which were validated by four linkage populations and 92 were new loci for grain length. We scanned the Ho (observed heterozygosity per locus) index of coupled-parents of crosses mapping the same QTL, based on linkage and association mapping, and identified two new genes for grain length. We named this approach as Ho-LAMap. A simulation study of six known genes showed that Ho-LAMap could mine genes rapidly across a wide range of experimental variables using deep-sequencing data. We used Ho-LAMap to clone a new gene, OsLG3, as a positive regulator of grain length, which could improve rice yield without influencing grain quality. Sequencing of the promoter region in 283 rice accessions from a wide geographic range identified four haplotypes that seem to be associated with grain length. Further analysis showed that OsLG3 alleles in the indica and japonica evolved independently from distinct ancestors and low nucleotide diversity of OsLG3 in indica indicated artificial selection. Phylogenetic analysis showed that OsLG3 might have much potential value for improvement of grain length in japonica breeding. The results demonstrated that Ho-LAMap is a potential approach for gene discovery and OsLG3 is a promising gene to be utilized in genomic assisted breeding for rice cultivar improvement.

The external application of nitrogen (N) fertilizers is an important practice for increasing crop production. However, the excessive use of fertilizers significantly increases production costs and causes environmental problems, making the improvement of crop N-use efficiency (NUE) crucial for sustainable agriculture in the future. Here we show that the rice (Oryza sativa) NUE quantitative trait locus DULL NITROGEN RESPONSE1 (qDNR1), which is involved in auxin homeostasis, reflects the differences in nitrate (⁠ $NO3−$⁠) uptake, N assimilation, and yield enhancement between indica and japonica rice varieties. Rice plants carrying the DNR1^indica allele exhibit reduced N-responsive transcription and protein abundance of DNR1. This, in turn, promotes auxin biosynthesis, thereby inducing AUXIN RESPONSE FACTOR-mediated activation of $NO3−$ transporter and N-metabolism genes, resulting in improved NUE and grain yield. We also show that a loss-of-function mutation at the DNR1 locus is associated with increased N uptake and assimilation, resulting in improved rice yield under moderate levels of N fertilizer input. Therefore, modulating the DNR1-mediated auxin response represents a promising strategy for achieving environmentally sustainable improvements in rice yield.