1. Conclusions and future work
Dissection of environmental and genetic factors leading to apical abortion in broccoli
呂學宇1、李勇毅2、許再文3、忻俐瑩1、魏雋瑀1、郭柏宇1、郭至賢1、傅士峰1
1Department of Biology, National Chunghua University of Education, Taiwan 彰化師範大學生物學系
2Botany Department, National Museum of Natural Science, Taiwan 自然科學博物館植物園
3Endemic Species Research Institute, Taiwan 特有生物研究保育中心
Abstract
3. Formation of lateral shoots after apical abortion in sensitive lines
Broccoli (Brassica oleracea var. italica) is a floral vegetable with an important nutritional value due to its content of dietary fiber, antioxidants and anti-carcinogenic compounds. Production and breeding of high-quality seeds and varieties is fundamental to modern agriculture management, leading to increase benefit of agronomic practices. Apical abortion in broccoli is a highly destructive disorder which occurs in transplants. However, little is known about the genetic and environmental factors that affect apical abortion. None of the molecular basis is proposed for selection of the broccoli varieties with resistance or susceptibility to apical abortion. In this study, we characterized the broccoli cultivars with healthy and aborted shoots by using comparative transcriptome (RNA-seq) at the early vegetative stage. Nearly-isogenic lines for broccoli plants with differential apical shoot-forming capacity were obtained from a local seed breeder. The tolerant line for apical abortion (BT001) and sensitive line (BS001) developed normally at 22/18℃ (day/night). However, the sensitive line showed significant apical abortion under 32/28℃. The result suggested that high temperature leads to apical abortion. Transcriptomic analysis was performed to characterize the differentially expressed genes between the two lines. Gene ontology analysis showed that response to heat and response to high light intensity was enriched in heat-tolerant lines. Genes involved in glucosinolate synthesis was enriched in heat-sensitive lines. Differential broccoli varieties may exhibit various apical shoot-forming capacities under high temperature. Apical abortion in broccoli may result from both environmental and genetic factors.
Fig. 3 Analysis of lateral shoot formation after after apical abortion in the broccoli tolerant- (BT01) and sensitive lines (BS01) ) at 22 ℃ and 32 ℃.
4. High-temperature-treated root tissues led to apical abortion
Results
1. High temperature resulted in apical abortion in sensitive broccoli lines
Fig. 1 Growth kinetics and shoot development of the apical abortion-tolerant (BT01) and -sensitive lines (BS01) at 22 ℃ and 32 ℃. The two broccoli lines were grown for at different period of time (30, 40 and 60d) post germination. Apical abortion-tolerant lines (BT01) exhibited normal shoot apex development at both 22℃ and 32 ℃. The sensitive lines (BS01) exhibited normal apex development at 22 ℃. Stunt shoot development was found in apical abortion-sensitive lines (BS01) at 32 ℃. The leaf numbers of the two broccoli lines were analyzed from 30 to 60 days at 22℃ and 32 ℃, respectively.
Fig. 4 Grafting analysis of the apical abortion-tolerant (BT01) and –sensitive lines (BS01) at at 22 ℃ and 32 ℃. The high-temperature –treated (32 ℃) broccoli lines served as root stocks while the sections were collected from the two lines treated with 22 ℃ or 32 ℃.
5. Transcriptomic analysis of apical abortion by RNA-seq
BT01-enriched gene annotation (22 ℃)
BT01/BS01 fold change>2
BS01-enriched gene annotation (22 ℃)
BS01/BT01 fold change>2 *
2. Anatomy of shoot apical meristems in broccoli lines with apical abortion
Fig. 2 Microscopic examination of shoot apical meristem in of the apical abortion-tolerant (BT01) and -sensitive lines (BS01) at 22 ℃ and 32 ℃. The two broccoli lines were grown for at different period of time (30, 40 and 60d) post germination. Stereo microscopy analysis of the shoot apex from the two broccoli lines (Upper panel). Light microscopy of shoot apical meristem of the two broccoli lines (Middle panel). Scanning electron micrography of the two lines (Lower panel).
Fig. 5 Transcriptomic analysis of apical abortion in broccoli by RNA-seq. The apical abortion-tolerant (BT01) and –sensitive broccoli lines (BS01) were grown at 22 ℃ for 4 week. RNA samples were extracted from the shoot apex from the two broccoli lines and subjected to high-throughput RNA-seq analysis. Differentially expressed genes with more than 2-fold change from BT01/BS01 and BS01/BT01 were defined as BT01-enriched and BS01 –enriched, respectively.
Conclusions and future work
Differential broccoli varieties may exhibit various apical shoot-forming capacities under high temperature. Apical abortion in broccoli may result from both environmental and genetic factors. Identification of molecular DNA marker by agrobiotechnology in this study will help local seed breeder to obtain healthy broccoli varieties.