A high-quality sponge gourd (Luffa cylindrica) genome.

Sponge gourd (Luffa cylindrica) is an important cultivated vegetable and medicinal plant in the family Cucurbitaceae. In this study, a draft genome sequence of the sponge gourd inbred line P93075 was analyzed. Using Illumina, PacBio, and 10× Genomics sequencing techniques as well as new assembly techniques such as FALCON and chromatin interaction mapping (Hi-C), a chromosome-scale genome of approximately 656.19 Mb, with an N50 scaffold length of 48.76 Mb, was generated. From this assembly, 25,508 protein-coding gene loci were identified, and 63.81% of the whole-genome consisted of transposable elements, which are major contributors to the expansion of the sponge gourd genome. According to a phylogenetic analysis of conserved genes, the sponge gourd lineage diverged from the bitter gourd lineage approximately 41.6 million years ago. Additionally, many genes that respond to biotic and abiotic stresses were found to be lineage specific or expanded in the sponge gourd genome, as demonstrated by the presence of 462 NBS-LRR genes, a much greater number than are found in the genomes of other cucurbit species; these results are consistent with the high stress resistance of sponge gourd. Collectively, our study provides insights into genome evolution and serves as a valuable reference for the genetic improvement of sponge gourd.

The Aborted Microspores (AMS)-Like Gene Is Required for Anther and Microspore Development in Pepper (Capsicum annuum L.).

Pepper (Capsicum annuum L.) is an economically important vegetable crop worldwide. Although many genes associated with anther and pollen development have been identified, little is known about the mechanism of pollen abortion in pepper. Here, we identified and isolated two putative aborted microspore (AMS) isoforms from pepper flowers: CaAMS1 and CaAMS2. Sequence analysis showed that CaAMS2 was generated by retention of the fourth intron in CaAMS1 pre-mRNA. CaAMS1 encodes a putative protein with a basic helix-loop-helix (bHLH) domain belonging to the MYC subfamily of bHLH transcription factors, and it is localized to the nucleus. Truncated CaAMS2-1 and CaAMS2-2 are produced by alternative splicing. Quantitative real-time PCR analysis showed that CaAMS (referred to CaAMS1 and CaAMS2-2) was preferentially expressed in stamens and its expression level gradually decreases with flower development. RNA in situ hybridization analysis showed that CaAMS is strongly expressed in the tapetum at the tetrad and uninucleate stages. Downregulation of CaAMS led to partial shortened filaments, shriveled, indehiscent stamens and abortive pollens in pepper flowers. Several genes involved in pollen exine formation were downregulated in defective CaAMS-silenced anthers. Thus, CaAMS seems to play an important role in pepper tapetum and pollen development by regulating a complex genetic network.