BackgroundSalinity is a stressful environmental factor that limits the productivity of crop plants, and roots form the major interface between plants and various abiotic stresses. Rice is a salt-sensitive crop and its polyploid shows advantages in terms of stress resistance. The objective of this study was to investigate the effects of genome duplication on rice root resistance to salt stress.ResultsBoth diploid rice (HN2026-2x and Nipponbare-2x) and their corresponding tetraploid rice (HN2026-4x and Nipponbare-4x) were cultured in half-strength Murashige and Skoog medium with 150 mM NaCl for 3 and 5 days. Accumulations of proline, soluble sugar, malondialdehyde (MDA), Na+ content, H+ (proton) flux at root tips, and the microstructure and ultrastructure in rice roots were examined. We found that tetraploid rice showed less root growth inhibition, accumulated higher proline content and lower MDA content, and exhibited a higher frequency of normal epidermal cells than diploid rice. In addition, a protective gap appeared between the cortex and pericycle cells in tetraploid rice. Next, ultrastructural analysis showed that genome duplication improved membrane, organelle, and nuclei stability. Furthermore, Na+ in tetraploid rice roots significantly decreased while root tip H+ efflux in tetraploid rice significantly increased.ConclusionsOur results suggest that genome duplication improves root resistance to salt stress, and that enhanced proton transport to the root surface may play a role in reducing Na+ entrance into the roots.

The breeding of polyploid rice made no breakthrough for a long time because of low seed set. The discovery and application of polyploid meiosis stability (PMeS) material played a pivotal role in solving this problem. Our results indicated that genome duplication led to different outcomes in different rice cultivars in terms of pollen fertility, viability, and the accumulation of important physiological substances such as free proline and endogenous hormones. Pollen from the PMeS HN2026-4X lines showed a high fertility and viability similar to those of HN2026-2X (4X indicates tetraploid while 2X indicates the diploid), whereas both rates decreased dramatically in Balilla-4X. The results of pollen microstructure and ultrastructure investigations suggested that the pollen development pattern in HN2026-4X appeared normal at all stages, but a lot of changes were discovered in Balilla-4X. Stable meiosis, timely tapetum degradation, and normal mitochondria development were critical factors insuring the high frequency pollen fertility of PMeS rice. The free proline content increased markedly in HN2026-4X as compared to HN2026-2X, but it was decreased for Balilla-4X. Genome duplication effects on regulating endogenous hormones accumulation in pollen were evident, resulting in the clear difference between PMeS HN2026-4X and Balilla-4X. The accumulation of IAA, ZR, and GA in mature pollen distinguished HN2026-4X from Balilla-4X, which was linked to normal pollen development. In particular, the excessive accumulation of ABA at the meiosis stage may be correlated to disorganized meiosis in Balilla-4X. All the results provided unequivocal evidence that genome duplication played specific roles in the normal pollen development of PMeS HN2026-4X.

He, Y.-C., Ge, J., Wei, Q., Jiang, A.-M., Gan, L., Song, Z.-J. and Cai, D.-T. 2011 Using a polyploid meiosis stability (PMeS) line as a parent improves embryo development and the seed set rate of a tetraploid rice hybrid. Can. J. Plant Sci. 91: 325–335. Polyploidy is widely accepted to play an important role in the evolution and breeding of plant species. However, a low seed set rate significantly hindered the development of polyploid rice breeding. Our results show that the seed set rate in polyploid meiosis stability (PMeS) line HN2026-4X was above 80%, but less than 40% in the other two tetraploid lines (4X indicates a tetraploid line and 2X indicates a diploid line). Furthermore, the seed set rate of Balilla-4X×HN2026-4X was also higher (67.18%) compared with that of Balilla-4X×NJ11-4X (37.26%), suggesting that the PMeS trait was transmitted to the next generation. The significantly higher seed set rate was attributed to the high pollen fertility and viability, as well as the normal meiosis of the HN2026-4X line as a male parent and also to successful embryogenesis. Investigations into embryo microstructure suggested that the embryo development pattern in Balilla-4X×HN2026-4X appeared normal at all stages, but many changes were discovered in Balilla-4X×NJ11-4X. The embryos were mainly defective at the four following stages: 1 d after pollination (DAP), 2–3 DAP, 4-5 DAP, and 10-15 DAP. The pattern of embryo developmental failure was similar in the two hybrids, but the abortive frequency in Balilla-4X×HN2026-4X was significantly lower than that of Balilla-4X×NJ11-4X at the respective stages. Additionally, aberrant fertilization, poor endosperm development, and abnormal embryo polarization also contributed to the low seed set in the hybrid of Balilla-4X×NJ11-4X. This study suggests that the PMeS line is a valuable resource, which could be used to develop tetraploid rice hybrids with superior yield.

Background Paris polyphylla is a herb widely used in traditional Chinese medicine to treat various diseases. Stem rot diseases seriously affected the yield of P. polyphylla in subtropical areas of China. Therefore, cost-effective, chemical-free, eco-friendly strategies to control stem rot on P. polyphylla are valuable and urgently needed. Results In this paper, we reported the biocontrol efficiency of Paenibacillus peoriae HJ-2 and its complete genome sequence. Strain HJ-2 could serve as a potential biocontrol agent against stem rot on P. polyphylla in the greenhouse and field. The genome of HJ-2 consists of a single 6,001,192 bp chromosome with an average GC content of 45% and 5,237 predicted protein coding genes, 39 rRNAs and 108 tRNAs. The phylogenetic tree indicated that HJ-2 is most closely related to P. peoriae IBSD35. Functional analysis of genome revealed numerous genes/gene clusters involved in plant colonization, biofilm formation, plant growth promotion, antibiotic and resistance inducers synthesis. Moreover, metabolic pathways that potentially contribute to biocontrol mechanisms were identified. Conclusions This study revealed that P. peoriae HJ-2 could serve as a potential BCA against stem rot on P. polyphylla. Based on genome analysis, the genome of HJ-2 contains more than 70 genes and 12 putative gene clusters related to secondary metabolites, which have previously been described as being involved in chemotaxis motility, biofilm formation, growth promotion, antifungal activity and resistance inducers biosynthesis. Compared with other strains, variation in the genes/gene clusters may lead to different antimicrobial spectra and biocontrol efficacies.