RESUMO
BACKGROUND: Stomatal variation, including guard cell (GC) density, size and chloroplast number, is often used to differentiate polyploids from diploids. However, few works have focused on stomatal variation with respect to polyploidization, especially for consecutively different ploidy levels within a plant species. For example, Allium tuberosum, which is mainly a tetraploid (2n = 4x = 32), is also found at other ploidy levels which have not been widely studied yet. RESULTS: We recently found cultivars with different ploidy levels, including those that are diploid (2n = 2x = 16), triploid (2n = 3x = 24), pseudopentaploid (2n = 34-42, mostly 40) and pseudohexaploid (2n = 44-50, mostly 48). GCs were evaluated for their density, size (length and width) and chloroplast number. There was no correspondence between ploidy level and stomatal density, in which anisopolyploids (approximately 57 and 53 stomata/mm2 in triploid and pseudopentaploid, respectively) had a higher stomatal density than isopolyploids (approximately 36, 43, and 44 stomata/mm2 in diploid, tetraploid and pseudohexaploid, respectively). There was a positive relationship between ploidy level and GC chloroplast number (approximately 44, 45, 51, 72 and 90 in diploid to pseudohexaploid, respectively). GC length and width also increased with ploidy level. However, the length increased approximately 1.22 times faster than the width during polyploidization. CONCLUSIONS: This study shows that GC size increased with increasing DNA content, but the rate of increase differed between length and width. In the process of polyploidization, plants evolved longer and narrower stomata with more chloroplasts in the GCs.
Assuntos
Cebolinha-Francesa , Estômatos de Plantas , Ploidias , Cebolinha-Francesa/genética , Tetraploidia , TriploidiaRESUMO
MAIN CONCLUSION: Natural 2n female gametes and transmission of parental heterozygosity by natural 2n gametes in Populus tomentosa are reported for the first time, which provides a new approach to polyploid breeding. Naturally occurring 2n pollen is widespread in Populus tomentosa and plays an important role in polyploid breeding. However, the competitiveness of 2n pollen is lower than that of haploid pollen during pollination and fertilization, so 2n pollen is less efficient at fertilizing haploid female gametes to produce polyploids. In theory, polyploids can also be obtained when 2n female gametes are fertilized by haploid pollen. Thus, the question becomes whether natural 2n female gametes exist in P. tomentosa, which can be answered by examining the genetic composition of natural 2n gametes. In this study, the origin of 87 triploids from the hybrid combination "X-2 × Z-5" was identified by SSR markers and 21% of natural 2n gametes were found to originate from female parents. Four SSR loci with low recombination rates were used to identify the genetic composition of natural 2n gametes. The results showed that the genetic composition of 2n female gametes was mainly characterized by SDR, while 2n male gametes were mainly produced by FDR. Moreover, the transmission of parental heterozygosity by natural 2n gametes, which is significantly different between female and male parents in FDR and SDR types, was analysed using 42 SSR primers. Here, we report naturally occurring 2n female gametes for the first time in P. tomentosa and reveal the genetic constitution and transmitted parental heterozygosity of these gametes. Our results provide a foundation for theoretical research into 2n gametes and their application in new polyploid breeding strategies.
Assuntos
Variação Genética , Repetições de Microssatélites/genética , Populus/genética , Cruzamento , Marcadores Genéticos/genética , Células Germinativas Vegetais , Heterozigoto , Pólen/genética , PoliploidiaRESUMO
Ehretia macrophylla Wall, known as wild loquat, is an ecologically, economically, and medicinally significant tree species widely grown in China, Japan, Vietnam, and Nepal. In this study, we have successfully generated a haplotype-resolved chromosome-scale genome assembly of E. macrophylla by integrating PacBio HiFi long-reads, Illumina short-reads, and Hi-C data. The genome assembly consists of two haplotypes, with sizes of 1.82 Gb and 1.58 Gb respectively, and contig N50 lengths of 28.11 Mb and 21.57 Mb correspondingly. Additionally, 99.41% of the assembly was successfully anchored into 40 pseudo-chromosomes. We predicted 58,886 protein-coding genes, of which 99.60% were functionally annotated from databases. We furthermore detected 2.65 Gb repeat sequences, 659,290 rRNAs, 4,931 tRNAs and 4,688 other ncRNAs. The high-quality assembly of the genome offers a solid basis for furthering the fields of molecular breeding and functional genomics of E. macrophylla.