Production and cytological characterization of a synthetic amphiploid derived from a cross between Oryza sativa and Oryza punctata

Genetic enhancement of okra [Abelmoschus esculentus (L.) Moench] germplasm through wide hybridization

Introduction

The introgression of genetic material from one species to another through wide hybridization and repeated back-crossing, plays an important role in genetic modification and enriching the cultivated gene-pool with novel genetic variations. Okra (Abelmoschus esculentus [(L.) Moench)] is a popular vegetable crop with high dietary fibre and protein, rich in essential amino acids, lysine and tryptophan. The wild Abelmoschus genepool has many desirable traits like ornamental value, short internodal length, more number of productive branches, extended bearing, perennation tendency, reduced fruit length (more consumer preferred trait), high mucilage content (medicinal value), abiotic stress tolerances such as drought, high temperature and biotic stress resistances such as okra Yellow Vein Mosaic Virus (YVMV) and Enation Leaf Curl Virus (ELCV) diseases. The repeated use of elite breeding lines led to narrowing of the genetic base of the okra crop, one of the major factors attributed to breakdown of resistance/ tolerance to biotic stresses. YVMV and ELCV are the two major diseases, causing significant yield loss in okra. Hence, wide hybridization was attempted to transfer tolerance genes from wild species to the cultivated genepool to widen the genetic base.

Material and methods

The screening of germplasm of wild Abelmoschus species at hotspots led to the identification of tolerant species (Abelmoschus pungens var. mizoramensis, A. enbeepeegeearensis, A. caillei, A. tetraphyllus and A. angulosus var. grandiflorus), which were further used in a wide-hybridization programme to generate interspecific hybrids with the cultivated okra. Presence of pre- and post-zygotic barriers to interspecific geneflow, differences in ploidy levels and genotype specific variations in chromosome numbers led to varying degrees of sterility in F1 plants of interspecific crosses. This was overcome by doubling the chromosome number of interspecific hybrids by applying Colchicine at the seedling stage. The 113 cross derivatives generated comprising amphidiploids in the F1 generation (30), F3 (14), one each in F2 and F4 generations, back cross generation in BC1F2 (03), BC1F3 (25), and BC2F3 (02), crosses between amphidiploids (27), multi-cross combinations (07) and inter-specific cross (between A. sagittifolius × A. moschatus subsp. moschatus) selfed derivatives at F8 generation (03) were characterized in the present study. Besides they were advanced through selfing and backcrossing.

Results and Discussion

The amphidiploids were found to possess many desirable genes with a considerable magnitude of linkage drag. Majority of the wide cross derivatives had an intermediate fruit morphology and dominance of wild characters viz., hispid fruits, stem, leaves, tough fruit fibre, vigorous perennial growth habit and prolonged flowering and fruiting. The fruit morphology of three BC progenies exhibited a high morphological resemblance to the cultivated okra, confirming successful transfer of useful genes to the cultivated okra genepool. The detailed morphological characteristics of the various combinations of Abelmoschus amphidiploids and the genetic enhancement of the genepool achieved in this process is reported here.

Full-length transcriptome reconstruction reveals genetic differences in hybrids of Oryza sativa and Oryza punctata with different ploidy and genome compositions

BACKGROUND

Allopolyploid breeding is an efficient technique for improving the low seed setting rate of autotetraploids in plant breeding and one of the most promising breeding methods. However, there have been few comprehensive studies of the posttranscriptional mechanism in allopolyploids.

RESULTS

By crossing cultivated rice (Oryza sativa, genome AA) with wild rice (Oryza punctata, genome BB), we created hybrid rice lines with different ploidy and genome compositions [diploid hybrid F01 (AB), allotetraploid hybrid F02 (AABB) and F03 (AAAB)]. The genetic differences of the hybrids and the mechanism of allopolyploid breeding dominance were revealed through morphological and cytological observations and single molecule real-time sequencing techniques. The tissues and organs of allotetraploid hybrid F02 exhibited "gigantism" and the highest levels of fertility. The numbers of non-redundant transcripts, gene loci and new isoforms in the polyploid rice lines were higher and the isoform lengths greater than those of the diploid line. Moreover, alternative splicing (AS) events occurred twice as often in the polyploid rice lines than the diploid line. During these events, intron retention dominated. Furthermore, a large number of new genes and isoforms specific to the lines of different ploidy were discovered.

CONCLUSIONS

The results indicated that alternative polyadenylation (APA) and AS events contributed to the complexity and superiority of polyploids in the activity of translation regulators, nucleic acid binding transcription factor activities and the regulation of molecular function. Therefore, these APA and AS events in allopolyploid rice were found to play a role in regulation. Our study provides new germplasm for polyploid rice breeding and reveals complex regulatory mechanisms that may be related to heterosis and fertility.

Study of Rhizosphere Microbial Community Structures of Asian Wild and Cultivated Rice Showed That Cultivated Rice Had Decreased and Enriched Some Functional Microorganisms in the Process of Domestication

Asian cultivated rice (Oryza sativa L.), domesticated from Asian wild rice, is a staple food crop for populations around the world. Asian cultivated rice has undergone physiological changes in the process of its evolution from Asian wild rice, and the closely related rhizosphere microorganisms may have changed in the process of plant domestication. However, the rhizosphere microorganisms of different Asian wild rice species and their related indica and japonica cultivated rice have not yet been illustrated clearly. This study aimed to illustrate the microbial community structures in the rhizosphere of Asian wild rice (common wild rice, nivara wild rice, medicinal wild rice, and spotted wild rice) and Asian cultivated rice (indica and japonica accessions) through the high-throughput sequencing of 16S rDNA, ITS amplifiers and metagenomic data. The results showed that there were significant differences between wild and cultivated rice in their rhizosphere microbial community structures. In view of the indica and japonica rice, the bacterial and fungal community structures of indica rice with the nivara wild rice and medicinal wild rice were more similar than the japonica rice species. The indica and japonica rice had the lowest proportion of Actinobacteria than the wild rice species, and indica rice has the highest relative abundance of Nitrospira. As for the microbial functions, methane metabolism and pyruvate metabolism were found to be the common pathway enriched in the rhizosphere of common and nivara wild rice in comparison with the indica and japonica rice; in addition, though it was found that the relative abundances of the pathogenic fungi in the rhizosphere soil of indica and japonica rice were significantly lower than that of the wild rice, the relative abundances of Magnaporthales and Ustilaginales were significantly higher in indica and japonica rice than that of the wild rice. This study is expected to provide a theoretical basis for the development and utilization of rhizosphere microbial resources for wild and cultivated rice.