Over the past 50 years, the understanding of meiosis has aged like a fine bottle of wine: the complexity is developing but the wine itself is still young. While emphasis in the plant kingdom has been placed on the model diploids Arabidopsis (Arabidopsis thaliana L.) and rice (Orzya sativa L.), our research has mainly focussed on the polyploid, bread wheat (Triticum aestivum L.). Bread wheat is an important food source for nearly two-thirds of the world's population. While creating new varieties can be achieved using existing or advanced breeding lines, we would also like to introduce beneficial traits from wild related species. However, expanding the use of non-adapted and wild germplasm in cereal breeding programs will depend on the ability to manipulate the cellular process of meiosis. Three important and tightly-regulated events that occur during early meiosis are chromosome pairing, synapsis and recombination. Which key genes control these events in meiosis (and how they do so) remains to be completely answered, particularly in crops such as wheat. Although the majority of published findings are from model organisms including yeast (Saccharomyces cerevisiae) and the nematode Caenorhabditis elegans, information from the plant kingdom has continued to grow in the past decade at a steady rate. It is with this new knowledge that we ask how meiosis will contribute to the future of cereal breeding. Indeed, how has it already shaped cereal breeding as we know it today?

/pdf/understanding-meiosis-and-the-implications-for-crop-25zz14h4g8.pdf

Understanding meiosis and the implications for crop improvement

The 2 species G. hirsutum and G. arboreum were crossed and triploid hybrid (AAD) was developed as a first step of crossing. The triploid is sterile and its hybridity was confirmed with morphological traits and DNA based SSR markers. The chromosome analysis at metaphase-I exhibited 13AA bivalents and 13D univalents at most of the PMC's studied which also confirmed its triploid nature. The mean chromosome pairing association was recorded as 12.90% (univalent), 10.45% (bivalent), 0.45% (trivalent), and 0.48% (tetravalent). The formation of multivalents depicted genome association between 2 species. The further utility of synthesized triploid with respect to the development of CLCuV resistant introgression genotypes is discussed

Development of an Interspecific Hybrid (Triploid) by Crossing Gossypium hirsutum and G. arboreum

Cytological and molecular investigations were undertaken for parent and progeny derived from a trispecific line [2(Gossypium arboreum × G. anomalum) × G. hirsutum var. BWR], which was crossed with G. hirsutum var. JLH168. Cytomorphological analysis of the F1 (G. arboreum × G. anomalum), its amphidiploid and progeny from trispecies hybrid showed distorted ploidy segregation with monovalents to hexavalents and high intergenomic (small A2 and large B1) allosynthetic chromosome pairing. Microsatellite analysis identified three fragments associated with G. arboreum and G. anomalum and six fragments associated with G. hirsutum in derivates of the trispecies line × G. hirsutum var. JLH168. Inter-Retrotransposon Amplified Polymorphism (IRAP) analysis revealed fragments of G. arboreum and G. anomalum, only in F1 and amphidiploid. Chromosomal association and microsatellite analysis of three progeny genotypes (i.e. haploid, hexaploid and tetraploid no. 1) confirmed that they share multigenomic background from the three cotton species (A2, AhDh and B1 genome). The interspecific hybrid cotton genotypes studied are likely to be useful for the introgression of genes from diploid species to commercial upland cultivars.

Interspecific hybridization in Gossypium L.: characterization of progenies with different ploidy-confirmed multigenomic backgrounds

Development and quality of pollen in Lachenalia cultivars with determination of genome size and chromosome number

棉属有丰富的种质资源，野生棉具有栽培种所缺乏的许多优良性状，为了将野生澳洲棉和绿顶棉的优良性状导入陆地棉，以期改良栽培种陆地棉。本研究通过陆地棉和C组野生澳洲棉远缘杂交获得杂种F1，并对其进行染色体加倍，将加倍成的异源六倍体与B组野生绿顶棉杂交，产生陆地棉、澳洲棉、绿顶棉的三元杂种，并对该三元杂种花粉母细胞减数分裂行为进行观察。结果表明：三元杂种减数分裂异常，主要表现在：后期染色体不均等分离，使得末期形成大量的不正常多分孢子，其中以五分体居多，这些多分孢子进一步发育为大量败育花粉粒，导致该杂种高度不育。本研究不仅为该三元杂种不育提供了直接原因，也为进一步探讨有效的育性恢复方法及棉花新种质的创制提供了理论依据和中间材料。  There are rich germplasm resources in Gossypium and wild cotton species possess many valuable agronomic traits which cultivated cotton always lacks. In order to introgress the useful traits from wild species G. australe and G. capitis-viridis into cultivated species for improving upland cotton, tetraploid G. hirsutum was crossed directly with C-genome species G. australe as the pollen-providing parent, creating a triploid hybrid. Chromosome doubling of this triploid hybrid leads to an allohexaploid which was then crossed with B-genome wild species G. capitis-viridis, resulting in trispecific hybrid (G. hirsutum, G. australe and G. capitis-viridis). The characteristic of chromosome behavior during meiosis of trispecific hybrid F1 was further investigated in this study. Results indicated that the meiosis of trispecific hybrid was abnormal, which mainly reflected that the chromosomes were divided unequally during the anaphase II; and many abnormal multispores appeared in the telophase II, which finally developed into abortive pollen grains, directly leading to the sterility of trispecific hybrid F1. This study provides the main reason of sterility for this hybrid and supplies the theory basis and the effective method for restoring the fertility and further creating new cotton intermediate germplasms.

Cytogenetic Study on Trispecific Hybrid from Gossypium hirsutum L., G. australe and G. capitis-viridis

Studies on meiosis in pollen mother cells (PMCs) of a triploid interspecific hybrid (3x = 39 chromosomes, AAD) between tetraploid Gossypium hirsutum (4n = 2x = 52,AADD) and diploid G. arboreum (2n = 2x = 26,AA) are reported. During meiotic metaphase I, 13 AA bivalents and 13 D univalents are expected in the hybrid. However, only 28% of the PMCs had this expected configuration. The rest of the PMCs had between 8 and 12 bivalents and between 12 and 17 univalents. Univalents lagged at anaphase I, and at metaphase II one or a group of univalents remained scattered in the cytoplasm and failed to assemble at a single metaphase plate. Primary bipolar spindles organized around the bivalents and multivalents. In addition to the primary spindle, several secondary and smaller bipolar spindles organized themselves around individual univalents and groups of univalents. Almost all (97%) of the PMCs showed secondary spindles. Each spindle functioned independently and despite their multiple numbers in a cell, meiosis I proceeded normally, with polyad formation. These observations strongly support the view that in plant meiocytes bilateral kinetochore symmetry is not required for establishing a bipolar spindle and that single unpaired chromosomes can initiate and stabilize the formation of a functional bipolar spindle.

Mosareza Vafaie-Tabar

Papers

Meiosis in a triploid hybrid of Gossypium: high frequency of secondary bipolar spindles at metaphase II.