Asparagus kiusianus, an important wild relative of cultivated asparagus (A. officinalis), exhibits resistance to stem blight disease caused by Phomopsis asparagi. However, the mechanisms underlying this resistance are not understood and no transcriptomic or genetic resources are available for this species. De novo transcriptome sequencing of A. officinalis and A. kiusianus stems was performed 24 h after inoculation with P. asparagi. In total, 35,259 and 36,321 transcripts were annotated in A. officinalis and A. kiusianus, respectively. 1,027 up-regulated and 752 down-regulated transcripts were differentially expressed in the two Asparagus species. RNA sequencing data were validated using quantitative real-time reverse transcription PCR. Several defense-related genes including peroxidase 4, cationic peroxidase SPC4-like, pathogenesis-related protein-1-like, and jasmonic acid biosynthesis and signaling-related genes including phospholipase D alpha 1, 12-oxophytodienoate reductase and jasmonate-induced protein 23 KD were up-regulated in A. kiusianus relative to A. officinalis. In addition, infected A. kiusianuns exhibited a substantial increase in jasmonic acid and methyl jasmonate relative to A. officinalis. Peroxidase activity was significantly elevated in infected A. kiusianus compared with infected A. officinalis. Our transcriptomic database provides a resource for identifying novel genes and molecular markers-associated with Phomopsis disease resistance and will facilitate breeding and improvement of cultivated asparagus varieties.
In Arabidopsis thaliana, the E-class SEPALLATA (SEP) genes are generally expressed across all floral whorls. These genes play fundamental roles in floral organ fate determination during development by interacting with other MADS-box gene products, such as those from A-, B-, and C-class genes. However, the function of SEP genes in orchid remains obscure. Here, we analyzed a mutant orchid cultivar with greenish flowers in Habenaria radiata and found that this phenotype is caused by the absence of SEP function. Wild type H. radiata flowers contain a column and two perianth whorls consisting of three greenish sepals, two white petals, and a lip (labellum). By contrast, the flowers of H. radiata cultivar ‘Ryokusei’ appear greenish, with three normal sepals in whorl 1, two greenish petals and a lip in whorl 2, and several sepaloid organs and a ventral column in whorls 3 and 4. We isolated two SEP-like genes (HrSEP-1 and HrSEP-2) and two AGAMOUS-like genes (HrAG-1 and HrAG-2) from wild type H. radiata and compared their expression in the wild type vs. the mutant cultivar. HrAG-1 and HrAG-2 were expressed in the column in the wild type, whereas these genes were expressed in the ventral column and in sepaloid organs that had been converted from a column in ‘Ryokusei.’ HrSEP-1 and HrSEP-2 were expressed in all floral organs in the wild type. However, in the mutant cultivar, HrSEP-2 was expressed in all floral organs, while HrSEP-1 expression was not detected. Thus, we analyzed the genomic structures of HrSEP-1 in the wild type and ‘Ryokusei’ and identified a retrotransposon-like element in its first exon in ‘Ryokusei.’ Yeast two-hybrid assays demonstrated that HrSEP-1 interacts with HrDEF, HrAG-1, and HrAG-2. These results indicate that the mutant phenotype of ‘Ryokusei’ flowers is caused by the loss of function of HrSEP-1. Therefore, this gene plays an important role in column, lip, and petal development in H. radiata flowers.
This data article reports de novo transcriptome analysis of resistant wild Asparagus kiusianus and susceptible A. officinalis plants 24 and 48 h post-inoculation (24 and 48 hpi) with Phomopsis asparagi. Differential gene expression (DGE) analysis demonstrated that several genes involved in secondary metabolites and plant-pathogen interactions are up-regulated in resistant wild A. kiusianus relative to susceptible A. officinalis. The assembled contig sequences generated in this study were used to search single nucleotide polymorphism (SNP) and insertion/deletion (InDel) distribution in A. kiusianus and A. officinalis plants. SNP and InDel data developed from this transcriptome analysis will be used to generate a high-density linkage map to facilitate further development of molecular marker-assisted selection in A. officinalis.
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