The MSI1 member OsRBAP1 gene, identified by a modified MutMap method, is required for rice height and spikelet fertility

To explore the molecular mechanisms underlying plant height regulation, we isolated and characterized a stably inherited semi-dwarf mutant bgsd-2 from the ethane methyl sulfonate (EMS) mutant progeny of 'Ping Tang Wild-type (PTWT)', a rice (Oryza sativa ssp. japonica) landrace in Guizhou. Transcriptome sequencing and qRT-PCR analyses showed that a number of cellulose and lignin-related genes involved in cell wall biogenesis were substantially downregulated in bgsd-2. MutMap-based cloning revealed the occurrence of a single amino acid substitution in the LOC_Os01g51300 gene, belonging to the MSI1 (multicopy suppressor of IRA1) member OsRBAP1. The bgsd-2 mutation occurred in the 3rd exon of OsRBAP1, resulting in a nonsense mutation of a codon shift from glycine (G) to glutamic acid (E) at residue 65. Protein localization analysis uncovered that the OsRBAP1 gene encodes a nuclear-localized protein and that the mutation in bgsd-2 may affect the stability of the OsRBAP1 protein. The CRISPR/Cas9 system was used to switch off OsRBAP1 in PTWT to obtain the knockout mutant osrbap1, which exhibited a severe reduction in height and fertility. Cytological observations suggest that the dwarfism of osrabp1 may be caused by reduced cell size and numbers, and that male sterility may be due to abnormal microspore development. Transcriptome analysis revealed that OsRBAP1 defects can repress the expression of numerous essential genes, which regulate multiple developmental processes in plants. Altogether, our results suggest that OsRBAP1 plays an important role in the regulation of rice height and spikelet fertility.

Comparative transcriptomic analysis reveals the regulatory mechanism of the gibberellic acid pathway of Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.) dwarf mutants

BACKGROUND

Tartary buckwheat is an important minor crop species with high nutritional and medicinal value and is widely planted worldwide. Cultivated Tartary buckwheat plants are tall and have hollow stems that lodge easily, which severely affects their yield and hinders the development of the Tartary buckwheat industry.

METHODS

Heifeng No. 1 seeds were treated with ethylmethanesulfonate (EMS) to generate a mutant library. The dwarf mutant ftdm was selected from the mutagenized population, and the agronomic characteristics giving rise to the dwarf phenotype were evaluated. Ultra-fast liquid chromatography-electrospray ionization tandem mass spectrometry (UFLC-ESI-MS/MS) was performed to determine the factors underlying the different phenotypes between the wild-type (WT) and ftdm plants. In addition, RNA sequencing (RNA-seq) was performed via the HiSeq 2000 platform, and the resulting transcriptomic data were analysed to identify differentially expressed genes (DEGs). Single-nucleotide polymorphism (SNP) variant analysis revealed possible sites associated with dwarfism. The expression levels of the potential DEGs between the WT and ftdm mutant were then measured via qRT-PCR and fragments per kilobase of transcript per million mapped reads (FPKM).

RESULT

The plant height (PH) of the ftdm mutant decreased to 42% of that of the WT, and compared with the WT, the mutant and had a higher breaking force (BF) and lower lodging index (LI). Lower GA4 and GA7 contents and higher contents of jasmonic acid (JA), salicylic acid (SA) and brassinolactone (BR) were detected in the stems of the ftdm mutant compared with the WT. Exogenous application of GAs could not revert the dwarfism of the ftdm mutant. On the basis of the transcriptomic analysis, 146 homozygous SNP loci were identified. In total, 12 DEGs with nonsynonymous mutations were ultimately identified, which were considered potential candidate genes related to the dwarf trait. When the sequences of eight genes whose expression was downregulated and four genes whose expression was upregulated were compared, SKIP14, an F-box protein whose sequence is 85% homologous to that of SLY1 in Arabidopsis, presented an amino acid change (from Ser to Asn) and was expressed at a lower level in the stems of the ftdm mutant compared with the WT. Hence, we speculated that this amino acid change in SKIP14 resulted in a disruption in GA signal transduction, indirectly decreasing the GA content and downregulating the expression of genes involved in GA biosynthesis or the GA response. Further studies are needed to determine the molecular basis underlying the dwarf phenotype of the ftdm mutant.

CONCLUSION

We report a Tartary buckwheat EMS dwarf mutant, ftdm, suitable for high-density planting and commercial farming. A significant decrease in GA4 and GA7 levels was detected in the ftdm mutant, and 12 DEGs expressed in the stems of the ftdm mutant were selected as candidates of the dwarfing gene. One nonsynonymous mutation was detected in the SKIP14 gene in the ftdm mutant, and this gene had a lower transcript level compared with that in the WT.

Identification of modifiers of the plant height in wheat using an induced dwarf mutant controlled by RhtB4c allele

In wheat, 25 Rht genes for dwarfness are known, which include both, GA-insensitive and GA-responsive genes. The GA-insensitive Rht genes have been widely used, although, their suitability under abiotic stress conditions has been questioned. This necessitated a search for alternative GA-responsive, spontaneous and induced dwarfing genes. We earlier reported an induced dwarf mutant ('dwarf mutant-3'; 44 cm), and the mutant allele was named Rht4c allele (2BL). This dwarf mutant was not suitable for cultivation due to its extra dwarf nature. Therefore, we searched for naturally occurring QTLs, which would modify the phenotype of 'dwarf-mutant-3' using 'mutant-assisted gene identification and characterization' (MAGIC) approach. For this purpose, the 'dwarf mutant-3' was crossed with a tall wheat cv. NP114 and homozygous mutant F2 plants (~ 25% of the progeny) were selected, which were phenotyped for plant height and genotyped using SSR markers. The data were utilized for QTL analysis and plant height. Six modifier QTLs were identified on chromosomes 2A, 2B and 4A. Two QTLs each on 2A and 2B were responsible for increase in plant height (described as 'enhancer modifiers'), whereas the remaining two QTLs located on 4A were responsible for reducing the plant height (described as 'suppressor modifiers'). It was hypothesized that the enhancer QTLs could be exploited for the development of semi-dwarf high yielding genotypes containing Rht4c allele. This is the first study of its kind in wheat demontsrating that the MAGIC approach could be used for identification of modifiers of the mutant phenotypes of other traits for wheat improvement.

A novel maize dwarf mutant generated by Ty1-copia LTR-retrotransposon insertion in Brachytic2 after spaceflight

Retrotransposon insertion in Brachytic2 generated a new incomplete recessive dwarf allele after spaceflight can moderately reduce plant height in heterozygous and potentially improve maize yield. Plant height and ear height are two important agronomic traits in maize breeding. In this study, two dwarf mutants short internode length1 (sil1) and short internode length2 (sil2) were obtained from two of 398 spaceflighted seeds of inbred line 18-599. The decrease in longitudinal cell number and cell length led to the shortened internodes of sil1 and sil2. A Ty1-copia LTR-retrotransposon, termed ZmRE-1, inserted in the fifth exon of Brachytic2 (Br2) was identified in sil1 and sil2 at exactly the same site, which indicated the transposition of ZmRE-1 probably correlated with the spaceflight. This new dwarf mutant allele was named as br2-sil in this study. The insertion of ZmRE-1 not only led to the loss of normal transcript of Br2 allele, but also reduced the transcript expression of br2-sil allele. Chop-qPCR displayed that the promoter region DNA methylation level of br2-sil allele in sil1 was higher than that of Br2 allele in WT-sil1. We speculated that the increased methylation level might downregulate the br2-sil expression. There was no difference in the seed-setting rate between sil1 and WT-sil1. Meanwhile, br2-sil could reduce plant and ear height effectively in Br2/br2-sil genotype without negative effects on grain yield. Therefore, the application of br2-sil in breeding has the potential to improve the grain yield per unit area through increasing the planting density.

A novel single-base mutation in CaBRI1 confers dwarf phenotype and brassinosteroid accumulation in pepper

Dwarfing is the development trend of pepper breeding. It is of great practical and scientific value to generate new dwarf germplasms, and identify new genes or alleles conferring dwarf traits in pepper. In our previous study, a weakly BR-insensitive dwarf mutant, E29, was obtained by EMS mutagenesis of the pepper inbred line 6421. It can be used as a good parent material for breeding new dwarf varieties. Here, we found that this dwarf phenotype was controlled by a single recessive gene. Whole-genome resequencing, dCAPs analysis, and VIGs validation revealed that this mutation was caused by a nonsynonymous single-nucleotide mutation (C to T) in CaBRI1. An enzyme activity assay, transcriptome sequencing, and BL content determination further revealed that an amino-acid change (Pro1157Ser) in the serine/threonine protein kinase and catalytic (S_TKc) domain of CaBRI1 impaired its kinase activity and caused the transcript levels of two important genes (CaDWF4 and CaROT3) participating in BR biosynthesis to increase dramatically in the E29 mutant, accompanied by significantly increased accumulation of brassinolide (BL). Therefore, we concluded that the novel single-base mutation in CaBRI1 conferred the dwarf phenotype and resulted in brassinosteroid (BR) accumulation in pepper. This study provides a new allelic variant of the height-regulating gene CaBRI1 that has theoretical and practical values for the breeding of the plants suitable for the facility cultivation and mechanized harvesting of pepper varieties.

Characterization of genome-wide variations induced by gamma-ray radiation in barley using RNA-Seq

Background

Artificial mutagenesis not only provides a new approach to increase the diversity of desirable traits for breeding new varieties but are also beneficial for characterizing the genetic basis of functional genes. In recent decades, many mutation genes have been identified which are responsible for phenotype changes in mutants in various species including Arabidopsis and rice. However, the mutation feature in induced mutants and the underlying mechanisms of various types of artificial mutagenesis remain unclear.

Results

In this study, we adopted a transcriptome sequencing strategy to characterize mutations in coding regions in a barley dwarf mutant induced by gamma-ray radiation. We detected 1193 genetic mutations in gene transcription regions introduced by gamma-ray radiation. Interestingly, up to 97% of the gamma irradiation mutations were concentrated in certain regions in chromosome 5H and chromosome 7H. Of the 26,745 expressed genes, 140 were affected by gamma-ray radiation; their biological functions included cellular and metabolic processes.

Conclusion

Our results indicate that mutations induced by gamma-ray radiation are not evenly distributed across the whole genome but located in several concentrated regions. Our study provides an overview of the feature of genetic mutations and the genes affected by gamma-ray radiation, which should contribute to a deeper understanding of the mechanisms of radiation mutation and their application in gene function analysis.