Fine mapping of the grain chalkiness quantitative trait locus qCGP6 reveals the involvement of Wx in grain chalkiness formation.

Grain chalkiness is an important index of rice appearance quality and is negatively associated with rice processing and eating quality. However, the genetic mechanism underlying chalkiness formation is largely unknown. To identify the genetic basis of chalkiness, 410 recombinant inbred lines (RILs) derived from two representative indica rice varieties, Shuhui498 (R498) and Yihui3551 (R3551), were used to discover quantitative trait loci (QTLs). The two parental lines and RILs were grown in three locations in China under three controlled fertilizer application levels. Analyses indicated that chalkiness was significantly affected by genotype, the environment, and the interaction between the two, and that heritability was high. Several QTLs were isolated, including the two stable QTLs qCGP6 and qCGP8. Fine mapping and candidate gene verification of qCGP6 showed that Wx may play a key role in chalkiness formation. Chromosomal segment substitution lines (CSSLs) and near-isogenic lines (NILs) carrying the Wxa or Wxin allele produced more chalky grain than the R498 parent. A similar result was also observed in the 3611 background. Notably, the effect of the Wx genotype on rice chalkiness was shown to be dependent on environmental conditions, and Wx alleles exhibited different sensitivities to shading treatment. Using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9), the Wxa promoter region was successfully edited; down-regulating Wx alleviates chalkiness formation in NILR498-Wxa. This study developed a new strategy for synergistic improvement of eating and appearance qualities in rice, and created a novel Wx allele with great potential in breeding applications.

Wide Grain 3, a GRAS Protein, Interacts with DLT to Regulate Grain Size and Brassinosteroid Signaling in Rice.

BACKGROUND: Grain size is a direct determinant of grain weight and yield in rice; however, the genetic and molecular mechanisms determining grain size remain largely unknown. FINDINGS: We identified a mutant, wide grain 3 (wg3), which exhibited significantly increased grain width and 1000-grain weight. Cytological analysis showed that WG3 regulates grain size by affecting cell proliferation. MutMap-based gene cloning and a transgenic experiment demonstrated that WG3 encodes a GRAS protein. Moreover, we found that WG3 directly interacts with DWARF AND LOW-TILLERING (DLT), a previously reported GRAS protein, and a genetic experiment demonstrated that WG3 and DLT function in a common pathway to regulate grain size. Additionally, a brassinosteroid (BR) sensitivity test suggested that WG3 has a positive role in BR signaling in rice. Collectively, our results reveal a new genetic and molecular mechanism for the regulation of grain size in rice by the WG3-DLT complex, and highlight the important functions of the GRAS protein complex in plants. CONCLUSION: WG3 functions directly in regulating grain size and BR signaling in rice.

OsBSK2, a putative brassinosteroid-signalling kinase, positively controls grain size in rice.

Grain size is an important trait that directly affects grain yield in rice; however, the genetic and molecular mechanisms regulating grain size remain unclear. In this study, we identified a mutant, grain length and grain weight 10 (glw10), which exhibited significantly reduced grain length and grain weight. Histological analysis demonstrated that GLW10 affects cell expansion, which regulates grain size. MutMap-based gene mapping and transgenic experiments demonstrated that GLW10 encodes a putative brassinosteroid (BR) signalling kinase, OsBSK2. OsBSK2 is a plasma membrane protein, and an N-myristoylation site is needed for both membrane localization and function. OsBSK2 directly interacts with the BR receptor kinase OsBRI1; however, genetic experiments have demonstrated that OsBSK2 may regulate grain size independent of the BR signalling pathway. OsBSK2 can form a homodimer or heterodimer with OsBSK3 and OsBSK4, and silencing OsBSK2, OsBSK3, and OsBSK4 reduce grain size. This indicates that OsBSKs seem to function as homodimers or heterodimers to positively regulate grain size in rice. OsBSK2/3/4 are all highly expressed in young panicles and spikelet hulls, suggesting that they control grain size. In summary, our results provide novel insights into the function of BSKs in rice, and identify novel targets for improving grain size during crop breeding.

Production and characterization of a disomic 1M/1D Triticum aestivum-Aegilops comosa substitution line.

PI 554419, formerly designated as Ae. uniaristata, showed significant difference with other Ae. uniaristata and Ae. comosa accessions in morphological traits at the seedling stage and its leaf color, length, and width behaved as an intermediate type. In this study, we reclassified PI 554419 as Ae. comosa subsp. comosa by comparing the fluorescence in situ hybridization (FISH) signals and the patterns of PCR-based landmark unique gene (PLUG) markers and conserved orthologous set (COS) markers of PI 554419 with other Ae. uniaristata and Ae. comosa accessions as well as the taxonomic character of spike morphology. A disomic 1M/1D substitution line NB 4-8-5-9 derived from PI 554419 was identified from a distant hybridization of Ae. comosa with common wheat (STM 10/CSph1b//CM 39///13 P2-6) by the molecular cytological method. Furthermore, the agronomic and seed morphological traits, as well as the flour processing quality properties of NB 4-8-5-9, were compared with those of its three common wheat parents in two different locations during the 2017-2018 growing seasons. The agronomical traits of NB 4-8-5-9 were similar to or even better than its parents. The seed size-related traits of NB 4-8-5-9 were better than those of all three parents, and the 1000-grain weight and grain width were close to those of Chuanmai 39 (CM 39) and 13 P2-6 and larger than those of CSph1b. The processing quality properties of NB 4-8-5-9 were more similar to those of 13 P2-6 and CSph1b but less similar to those of CM 39. The 1M/1D substitution line NB 4-8-5-9 could further be used for developing translocation lines with 1M segment. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-021-01207-2.