Allelic variations of the Wx locus in cultivated rice and their use in the development of hybrid rice in China.

To make better use of global germplasm resources for improving the eating quality of hybrid rice, using the resequencing data from the 3,000 rice genomes project (3K RGP), the allelic variations of the rice Wx locus were analysed. With the exception of five rare alleles discovered for the first time in our study, most of these alleles were known alleles of Wx. Furthermore, a set of Kompetitive allele-specific PCR (KASP) markers based on these Wx alleles have been developed, and thirty-six main parents of hybrid rice from 1976 to 2018 were selected for Wx genotyping. The results showed that only three Wx alleles existed in the main parents of hybrids, and the allelic combination of the hybrids changed from Wxa/Wxb and Wxlv/Wxb to Wxb/Wxb with the development of hybrid rice. Wxb is widely used in the male parents of hybrid rice. Wxa and Wxlv were used in the female parents of early hybrid rice, and they were gradually replaced by Wxb. In the future, more favourable Wx alleles from cultivated rice should be identified, introduced, and effectively used to improve hybrid rice quality

Mutation of the RESURRECTION1 Locus of Arabidopsis Reveals an Association of Cuticular Wax with Embryo Development

Insertional mutagenesis of Arabidopsis (Arabidopsis thaliana) was used to identify a novel recessive mutant, designated resurrection1 (rst1), which possesses a dramatic alteration in its cuticular waxes and produces shrunken nonviable seeds due to arrested embryo development. The RST1 gene sequence associated with these phenotypes was verified by three independent, allelic, insertion mutants, designated rst1-1, rst1-2, and rst1-3, with inserts in the first exon, 12th intron, and fourth exon, respectively. These three rst1 allelic mutants have nearly identical alterations in their wax profiles and embryo development. Compared to wild type, the wax on rst1 inflorescence stems is reduced nearly 60% in total amount, has a proportional reduction in aldehydes and aldehyde metabolites, and has a proportional increase in acids, primary alcohols, and esters. Compared to wild type, the C(29) alkanes on rst1 are nearly 6-fold lower, and the C(30) primary alcohols are 4-fold higher. These results indicate that rst1 causes shunting of most wax precursors away from alkane synthesis and into the primary-alcohol-producing branch of the pathway. In contrast to stems, the wax on rst1 mutant leaves increased roughly 43% in amount relative to the wild type, with the major increase occurring in the C(31) and C(33) alkanes. Unique among known wax mutants, approximately 70% of rst1 seeds are shrunken and nonviable, with these being randomly distributed within both inflorescence and silique. Viable seeds of rst1 are slightly larger than those of wild type, and although the viable rst1 seeds contain more total triacylglycerol-derived fatty acids, the proportions of these fatty acids are not significantly different from wild type. Shrunken seeds contain 34% of the fatty acids of wild-type seeds, with proportionally more palmitic, stearic, and oleic acids, and less of the longer and more desaturated homologs. Histological analysis of aborted rst1 seeds revealed that embryo development terminates at the approximate heart-shaped stage, whereas viable rst1 and wild-type embryos develop similarly. The RST1 gene encodes a predicted 1,841-amino acid novel protein with a molecular mass of 203.6 kD and a theoretical pI of 6.21. The RST1 transcript was found in all tissues examined including leaves, flowers, roots, stems, and siliques, but accumulation levels were not correlated with the degree to which different organs appeared affected by the mutation. The new RST1 gene reveals a novel genetic connection between lipid synthesis and embryo development; however, RST1's exact role is still quite unknown. The degree to which RST1 is associated with lipid signaling in development is an important focus of ongoing studies

Genomic structure and evolution of the Pi2/9 locus in wild rice species

Rice blast, caused by the fungal pathogen Magnaporthe oryzae, is a devastating disease of rice worldwide. Among the 85 mapped resistance (R) genes against blast, 13 have been cloned and characterized. However, how these genes originated and how they evolved in the Oryza genus remains unclear. We previously cloned the rice blast R-genes Pi2, Pi9, and Piz-t, and analyzed their genomic structure and evolution in cultivated rice. In this study, we determined the genomic sequences of the Pi2/9 locus in four wild Oryza species representing three genomes (AA, BB and CC). The number of Pi2/9 family members in the four wild species ranges from two copies to 12 copies. Although these genes are conserved in structure and categorized into the same subfamily, sequence duplications and subsequent inversions or uneven crossing overs were observed, suggesting that the locus in different wild species has undergone dynamic changes. Positive selection was found in the leucine-rich repeat region of most members, especially in the largest clade where Pi9 is included. We also provide evidence that the Pi9 gene is more related to its homologues in the recurrent line and other rice cultivars than to those in its alleged donor species O. minuta, indicating a possible origin of the Pi9 gene from O. sativa. Comparative sequence analysis between the four wild Oryza species and the previously established reference sequences in cultivated rice species at the Pi2/9 locus has provided extensive and unique information on the genomic structure and evolution of a complex R-gene cluster in the Oryza genus

The SINA E3 Ligase OsDIS1 Negatively Regulates Drought Response in Rice1[C][W][OA]

Ubiquitin-regulated protein degradation is a critical regulatory mechanism that controls a wide range of biological processes in plants. Here, we report that OsDIS1 (for Oryza sativa drought-induced SINA protein 1), a C3HC4 RING finger E3 ligase, is involved in drought-stress signal transduction in rice (O. sativa). The expression of OsDIS1 was up-regulated by drought treatment. In vitro ubiquitination assays showed that OsDIS1 possessed E3 ubiquitin ligase activity and that the conserved region of the RING finger was required for the activity. Transient expression assays in Nicotiana benthamiana leaves and rice protoplasts indicated that OsDIS1 was localized predominantly in the nucleus. Overexpression of OsDIS1 reduced drought tolerance in transgenic rice plants, while RNA interference silencing of OsDIS1 enhanced drought tolerance. Microarray analysis revealed that a large number of drought-responsive genes were induced or suppressed in the OsDIS1 overexpression plants under normal and drought conditions. Yeast two-hybrid screening showed that OsDIS1 interacted with OsNek6 (for O. sativa NIMA-related kinase 6), a tubulin complex-related serine/threonine protein kinase. Coexpression assays in N. benthamiana leaves indicated that OsNek6 was degraded by OsDIS1 via the 26S proteasome-dependent pathway and that this degradation was abolished by the OsDIS1(H71Y) mutation, which is essential for its E3 ligase activity. Together, these results demonstrate that OsDIS1 plays a negative role in drought stress tolerance through transcriptional regulation of diverse stress-related genes and possibly through posttranslational regulation of OsNek6 in rice