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.
Lettuce (Lactuca sativa L.) bolting is often limiting in agricultural production as stem elongation followed by flower bud differentiation results in unmarketable plants. Thus, to solve this problem, it is important to elucidate the molecular mechanisms controlling flowering. To investigate the relationship between gene expression and flowering in lettuce, homologs of flowering-related genes were isolated and their expression over time was analyzed in three cultivars and in one breeding line by using quantitative real-time PCR. In plants grown in the field, the expression of the lettuce homologues APETALA 1 (LsAP1L) and LEAFY (LsLFYL) in the shoot apex correlated with flower bud formation, and FLOWERING LOCUS T (LsFT) expression increased during the transition from vegetative to reproductive growth. The transcription of FLOWERING LOCUS D (LsFLDL), FVE (LsFVEL), and LUMINIDEPENDENS (LsLDL) also increased with flowering. Our previous study showed that LsFT was upregulated during lettuce flowering induced under controlled high temperature conditions. Results from both studies suggest that LsFT is involved in lettuce flowering, both in natural and controlled conditions. This is also the first report on the expression of other flowering-related genes along with flowering of lettuce grown in the field.
Phomopsis asparagi is one of the most serious fungal pathogens, which causes stem blight disease in Asparagus officinalis (AO), adversely affecting its production worldwide. Recently, development of novel asparagus varieties using wild Asparagus genetic resources with natural P. asparagi resistance has become a priority in Japan due to the lack of resistant commercial AO cultivars. In the present study, comparative metabolome and transcriptome analyses of susceptible AO and resistant wild A. kiusianus (AK) 24 and 48 h post-inoculated (AOI_24 hpi, AOI_48 hpi, AKI_24 hpi and AKI_48 hpi, respectively) with P. asparagi were conducted to gain insights into metabolic and expression changes associated with the AK species. Following the infection, the resistant wild AK showed rapid metabolic changes with increased levels of flavonoids and steroidal saponins, and decreased asparagusic acid glucose ester content, compared with the susceptible AO plants. Transcriptome data revealed a total of 21l differentially expressed genes (DEGs) as the core gene set that displayed upregulation in the resistant AK versus susceptible AO after infection with P. asparagi. KEGG pathway analysis of these DEGs identified 11 significantly enriched pathways, including flavonoid biosynthesis and primary metabolite metabolism, in addition to plant signaling and defense-related pathways. In addition, comparative SNP and Indel distributions in susceptible AO and resistant AK plants were evaluated using the latest A. officinalis reference genome Aspof.V1. The data generated in this study are important resources for advancing the Asparagus breeding programs, and for investigations of genetic linkage map, phylogenetic diversity and plant defense-related genes.
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