BackgroundSacred lotus is a basal eudicot with agricultural, medicinal, cultural and religious importance. It was domesticated in Asia about 7,000 years ago, and cultivated for its rhizomes and seeds as a food crop. It is particularly noted for its 1,300-year seed longevity and exceptional water repellency, known as the lotus effect. The latter property is due to the nanoscopic closely packed protuberances of its self-cleaning leaf surface, which have been adapted for the manufacture of a self-cleaning industrial paint, Lotusan.ResultsThe genome of the China Antique variety of the sacred lotus was sequenced with Illumina and 454 technologies, at respective depths of 101× and 5.2×. The final assembly has a contig N50 of 38.8 kbp and a scaffold N50 of 3.4 Mbp, and covers 86.5% of the estimated 929 Mbp total genome size. The genome notably lacks the paleo-triplication observed in other eudicots, but reveals a lineage-specific duplication. The genome has evidence of slow evolution, with a 30% slower nucleotide mutation rate than observed in grape. Comparisons of the available sequenced genomes suggest a minimum gene set for vascular plants of 4,223 genes. Strikingly, the sacred lotus has 16 COG2132 multi-copper oxidase family proteins with root-specific expression; these are involved in root meristem phosphate starvation, reflecting adaptation to limited nutrient availability in an aquatic environment.ConclusionsThe slow nucleotide substitution rate makes the sacred lotus a better resource than the current standard, grape, for reconstructing the pan-eudicot genome, and should therefore accelerate comparative analysis between eudicots and monocots.

Sex determination in papaya is controlled by a recently evolved XY chromosome pair, with two slightly different Y chromosomes controlling the development of males (Y) and hermaphrodites (Y h ).To study the events of early sex chromosome evolution, we sequenced the hermaphrodite-specific region of the Y h chromosome (HSY) and its X counterpart, yielding an 8.1-megabase (Mb) HSY pseudomolecule, and a 3.5-Mb sequence for the corresponding X region. The HSY is larger than the X region, mostly due to retrotransposon insertions. The papaya HSY differs from the X region by two large-scale inversions, the first of which likely caused the recombination suppression between the X and Y h chromosomes, followed by numerous additional chromosomal rearrangements. Altogether, including the X and/or HSY regions, 124 transcription units were annotated, including 50 functional pairs present in both the X and HSY. Ten HSY genes had functional homologs elsewhere in the papaya autosomal regions, suggesting movement of genes onto the HSY, whereas the X region had none. Sequence divergence between 70 transcripts shared by the X and HSY revealed two evolutionary strata in the X chromosome, corresponding to the two inversions on the HSY, the older of which evolved about 7.0 million years ago. Gene content differences between the HSY and X are greatest in the older stratum, whereas the gene content and order of the collinear regions are identical. Our findings support theoretical models of early sex chromosome evolution.Carica papaya | DNA sequencing | molecular evolution | sex chromosomes S ex chromosomes have evolved independently in diverse lineages of animals and plants, and new dioecious species are still evolving (1, 2). Evidence of homology between nascent sex chromosome pairs in flowering plants and fish (3-6) supports the notion that sex chromosomes evolved from autosomes that gained sex determination genes. The key event in sex chromosome evolution is the suppression of recombination between the sex-determining regions of ancestrally homologous chromosome pairs, which limits one chromosome of the pair to one sex, producing XY (male heterogametic) or ZW (female heterogametic) systems. Evolutionary models predict that a lack of recombination allows for Y-or W-specific characteristics to accumulate, through the reduced efficacy of selection on these chromosomes (7,8), leading to the Y and W chromosomes accumulating deleterious mutations and transposable elements, and ultimately undergoing genetic degeneration, through the loss of genes or gene functions, as observed in mammals, Drosophila, birds, fishes, and snakes (9, 10). In some animals and plants, the greater number of mitotic cell divisions in spermatogenesis than oogenesis also leads to Y chromosomes having a higher mutation rate than autosomes or X chromosomes (11)(12)(13)(14) and is predicted to further contribute to greater changes of the evolving Y (or W) chromosome than the X (or Z) chromosome.To test these predictions of repetitive sequence accumulation, chromosoma...

Sex in papaya is controlled by a pair of nascent sex chromosomes. Females are XX, and two slightly different Y chromosomes distinguish males (XY) and hermaphrodites (XY h ). The hermaphrodite-specific region of the Y h chromosome (HSY) and its X chromosome counterpart were sequenced and analyzed previously. We now report the sequence of the entire male-specific region of the Y (MSY). We used a BAC-by-BAC approach to sequence the MSY and resequence the Y regions of 24 wild males and the Y h regions of 12 cultivated hermaphrodites. The MSY and HSY regions have highly similar gene content and structure, and only 0.4% sequence divergence. The MSY sequences from wild males include three distinct haplotypes, associated with the populations' geographic locations, but gene flow is detected for other genomic regions. The Y h sequence is highly similar to one Y haplotype (MSY3) found only in wild dioecious populations from the north Pacific region of Costa Rica. The low MSY3-Y h divergence supports the hypothesis that hermaphrodite papaya is a product of human domestication. We estimate that Y h arose only ∼4000 yr ago, well after crop plant domestication in Mesoamerica >6200 yr ago but coinciding with the rise of the Maya civilization. The Y h chromosome has lower nucleotide diversity than the Y, or the genome regions that are not fully sex-linked, consistent with a domestication bottleneck. The identification of the ancestral MSY3 haplotype will expedite investigation of the mutation leading to the domestication of the hermaphrodite Y h chromosome. In turn, this mutation should identify the gene that was affected by the carpel-suppressing mutation that was involved in the evolution of males.

Somatic embryogenesis (SE) is the developmental reprogramming of somatic cells toward the embryogenesis pathway and is a notable illustration of cell totipotency. To identify genes involved in SE, subtractive polymerase chain reaction (PCR) was performed to generate transcripts highly enriched for SE-related genes, using cDNA prepared from a mixture of embryogenic callus and pre-globular somatic embryos, as the tester, and cDNA from non-embryogenic callus, as the driver. After differential screening and subsequent confirmation by reverse Northern blot analysis, a total of 671 differentially expressed cDNA fragments were identified, and 242 uni-genes significantly up-regulated during cotton SE were recovered, as confirmed by Northern blot and reverse-transcription PCR analysis of representative cases, including most previously published SE-related genes in plants. In total, more than half had not been identified previously as SE-related genes, including dominant crucial genes involved in transcription, post-transcription, and transportation, and about one-third had not been reported previously to GenBank or were expected to be unknown, or newly identified genes. We used cDNA arrays to further investigate the expression patterns of these genes in differentiating gradient culture, ranging from pro-embryogenic masses to somatic embryos at every stage. The cDNA collection is composed of a broad repertoire of SE genes which is an important resource for understanding the genetic interactions underlying SE signaling and regulation. Our results suggested that a complicated and concerted mechanism involving multiple cellular pathways is responsible for cotton SE. This report represents a systematic and comprehensive analysis of genes involved in the process of somatic embryogenesis.

Sea-island cotton (Gossypium barbadense L.) is one of the most valuable cotton species due to its silkiness, luster, long staples, and high strength, but its fiber development mechanism has not been surveyed comprehensively. We constructed a normalized fiber cDNA library (from -2 to 25 dpa) of G. barbadense cv. Pima 3-79 (the genetic standard line) by saturation hybridization with genomic DNA. We screened Pima 3-79 fiber RNA from five developmental stages using a cDNA array including 9,126 plasmids randomly selected from the library, and we selected and sequenced 929 clones that had different signal intensities between any two stages. The 887 high-quality expressed sequence tags obtained were assembled into 645 consensus sequences (582 singletons and 63 contigs), of which 455 were assigned to functional categories using gene ontology. Almost 50% of binned genes belonged to metabolism functional categories. Based on subarray analysis of the 887 high-quality expressed sequence tags with 0-, 5-, 10-, 15-, and 20-dpa RNA of Pima 3-79 fibers and a mixture of RNA of nonfiber tissues, seven types of expression profiles were elucidated. Furthermore our results showed that phytohormones may play an important role in the fiber development.