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.

Seedlessness is a valuable agronomic trait in watermelon (Citrullus lanatus) breeding. Conventional less seed watermelons are mainly triploid, which has many disadvantages due to unbalanced genome content. Less seed watermelon can be achieved at the diploid level when certain reproductive genes are mutated or by chromosome translocation, which leads to defects during meiosis. However, the formation mechanism of diploid less seed watermelons remains largely unknown. Here, we identified a spontaneous mutant line, watermelon line “148”, which can set seeds normally when self-pollinated. A total of 148 × JM F1 hybrid plants exhibited seed number reductions to 50.3% and 47.3% of those of the two parental lines, respectively, which are considered to be less seed. Examination of pollen viability and hybridization experiments revealed that F1 hybrids produce semisterile pollen and ovules. Further cytological observations indicated that semisterility was a result of a reciprocal translocation of chromosomes, which exhibited one quadrivalent ring of four chromosomes at prometaphase I during meiosis. RT-qPCR analysis indirectly confirmed that the semisterile phenotype is caused by chromosome translocation rather than disruption of specific meiotic gene expression. F2 population genetic analysis indicated that the “148” watermelon line is a homozygous translocation and that the less seed phenotype of the F1 hybrid is prompted by one chromosome fragment translocation. The translocated fragment was further fine mapped to a 2.09 Mb region on chromosome 6 by whole-genome resequencing and genetic map cloning procedures. Our work revealed that a 2.09 Mb chromosome fragment translocation on chromosome 6, causing meiotic defects at metaphase I during meiosis, leads to diploid less seed watermelon. Our findings provide a new promising method for less seed watermelon breeding at the diploid level, as well as a fragment size reference for breeding less seed watermelon through artificially induced chromosome translocation.

The chickpea (Cicer arietinum L.) is the primary cultivated rain fed crop in the Xinjiang region of Northwest China. In 2007, chickpeas suffered an epidemic disease that caused significant economic losses. To identify the causative agent, debris and seeds of infected chickpea plants were collected from cultivated fields. We isolated and purified the responsible pathogen and tested its pathogenicity both in greenhouse and in the field. Morphological analysis using tissue culture as well as molecular techniques confirmed that the pathogen was the blight fungus Ascochyta rabiei.

The homeodomain–leucine zipper(HD-ZIP) gene family is involved in a variety of physiological processes in plants and plays a number of roles in rice. However, the analysis of this gene family in rice (Oryza sativa L.) is not comprehensive. The genome-wide characterization of HD-ZIP family was explored by using high-quality rice genome sequence combined with transcriptome. The HD-ZIP superfamily has four subfamilies in rice, including 31 HOX gene members in subfamilies I, II, and III, and nine rice outermost cell-specific gene (ROC) members in subfamily IV. Four subfamily members can interact with many reproductive and developmental related proteins, and subfamily II is regulated by miR396 family. We explored the expression patterns of HD-ZIPs in different rice tissues and analysis of high temperature and low temperature stress by RT-PCR showed that HD-ZIPs played an important role in the early stage of stress. The transcriptome results of diploid and tetraploid grains at different development stages showed that most HD-ZIP members were highly expressed in the early stage of grain development, and the expression of some members in tetraploid glumes was significantly higher than that in diploid glumes. These findings indicate the evolutionary process, characteristics and expression profile of HD-ZIP gene family in rice, and reveal their role in rice development and response to abiotic stress.