Yoko Mine

RNA-sequencing-based transcriptome and biochemical analyses of steroidal saponin pathway in a complete set of Allium fistulosum-A. cepa monosomic addition lines.

The genus Allium is a rich source of steroidal saponins, and its medicinal properties have been attributed to these bioactive compounds. The saponin compounds with diverse structures play a pivotal role in Allium’s defense mechanism. Despite numerous studies on the occurrence and chemical structure of steroidal saponins, their biosynthetic pathway in Allium species is poorly understood. The monosomic addition lines (MALs) of the Japanese bunching onion (A. fistulosum, FF) with an extra chromosome from the shallot (A. cepa Aggregatum group, AA) are powerful genetic resources that enable us to understand many physiological traits of Allium. In the present study, we were able to isolate and identify Alliospiroside A saponin compound in A. fistulosum with extra chromosome 2A from shallot (FF2A) and its role in the defense mechanism against Fusarium pathogens. Furthermore, to gain molecular insight into the Allium saponin biosynthesis pathway, high-throughput RNA-Seq of the root, bulb, and leaf of AA, MALs, and FF was carried out using Illuminas HiSeq 2500 platform. An open access Allium Transcript Database (Allium TDB, http://alliumtdb.kazusa.or.jp) was generated based on RNA-Seq data. The resulting assembled transcripts were functionally annotated, revealing 50 unigenes involved in saponin biosynthesis. Differential gene expression (DGE) analyses of AA and MALs as compared with FF (as a control) revealed a strong up-regulation of the saponin downstream pathway, including cytochrome P450, glycosyltransferase, and beta-glucosidase in chromosome 2A. An understanding of the saponin compounds and biosynthesis-related genes would facilitate the development of plants with unique saponin content and, subsequently, improved disease resistance.

Quantitative trait loci (QTL) controlling plant architecture traits in a Solanum lycopersicum × S. pimpinellifolium cross

Plant architecture is an important determinant of tomato yield because it affects light distribution within a crop canopy. One hundred and eleven lines of a BC1F8 population developed from Solanum lycopersicum ‘M570018’ and its wild relative Solanum pimpinellifolium (PI124039) were grown in a glasshouse in spring and autumn, and plant architecture traits evaluated at two leaf positions: the last leaf before floral initiation (F leaf) and the largest leaf (L leaf). QTL analysis was performed using QTLNetwork 2.1; 23 additive QTLs and seven epistatic QTLs were detected for 13 of 16 traits measured in this study. On chromosomes 2 and 12, QTLs for the leaf drooping angle (DRAN) of the F leaf (fdran2 and fdran12) co-located with QTLs for canopy size (CAN) at each leaf position of the F and L leaves (fcan2 and lcan2, fcan12 and lcan12). On chromosome 3, QTLs for leaf length (LL) of the F and L leaves (fll3 and lll3) co-located with the epistatic QTL for CAN at the L leaf (lcan3). QTLs for plant height (PH) were detected on chromosome 2, 3, 4, and 6; all of these QTLs (ph2, ph3, ph4, and ph6) decreased PH in the presence of Solanum lycopersicum (SL) alleles. QTLs for total leaf number and internode length were detected on chromosomes 3 and 4; tln3 and int4 mapped in the vicinity of ph3 and ph4, respectively. The co-localization of QTLs associated with CAN, DRAN, and LL suggests canopy size is determined by both leaf length and leaf drooping angle in tomato.