Transcriptomic and functional analysis of cucumber (Cucumis sativus L.) fruit phloem during early development

Abstract

The phloem of the Cucurbitaceae has long been a subject of interest due to its complex nature and the economic importance of the family. As in a limited number of other families, cucurbit phloem is bicollateral, i.e. with sieve tubes on both sides of the xylem. To date little is known about the specialized functions of the internal phloem (IP) and external phloem (EP). Here, a combination of microscopy, fluorescent dye transport analysis, micro-computed tomography, laser capture microdissection and RNA-sequencing (RNA-Seq) were used to study the functions of IP and EP in the vascular bundles (VBs) of cucumber fruit. There is one type of VB in the peduncle, but four in the fruit: peripheral (PeVB), main (MVB), carpel (CVB) and placental (PlVB). The VBs are bicollateral, except for the CVB and PlVB. Phloem mobile tracers and C applied to leaves are transported primarily in the EP, and to a lesser extent in the IP. RNA-Seq data indicate preferential gene transcription in the IP related to differentiation/development, hormone transport, RNA or protein modification/processing/transport, and nitrogen compound metabolism and transport. The EP preferentially expresses genes for stimulus/stress, defense, ion transport and secondary metabolite biosynthesis. The MVB phloem is preferentially involved in photoassimilate transport, unloading and long-distance signaling, while the PeVB plays a more substantial role in morphogenesis and/or development and defense response. CVB and PlVB transcripts are biased toward development of reproductive organs. These findings provide an integrated view of the differentiated structure and function of the vascular tissue in cucumber fruit.

Comparative transcriptome analysis reveals the response mechanism of Cf-16-mediated resistance to Cladosporium fulvum infection in tomato

“…Transcriptome sequencing (RNA-Seq) has strongly accelerated research on host-pathogen interactions in plants such as rice [31], maize [32], cucumber [33], watermelon [34] and strawberry [35]. Avr4/Cf-4and Avr9/Cf-9-dependent defense gene expression has been confirmed by cDNA-AFLP (cDNA-amplified fragment length polymorphism) analysis [36].…”

Complexity untwined: The structure and function of cucumber (Cucumis sativus L.) shoot phloem

“…Similarly, in the present study, PP2 was also widely found in cucumber shoot phloem based on LCM‐RNA‐seq data (Figure S5). Compared with cucumber fruit phloem (see figure S9a in Sui et al ., 2018), a total of 29 PP2 genes were expressed in distinct patterns in the IP and EP tissues of petiole and stem (Figure S5), except for two PP2 genes, Csa1G421930 and Csa1G703580 (no expression in all four tissues), which may result from different functional roles of the two types of shoot phloem, IP and EP.…”

“…The method of 14 CO 2 labeling was performed according to Sui et al (2018). After exposing the lamina to 14 CO 2 and allowing transport to occur for 6 h, the adjoining stem was cut and blotted by several times in quick succession on to filter paper, then the dried filter paper was pressed on to an X-ray film for 20 days.…”

Cucurbit Genomics Database (CuGenDB): a central portal for comparative and functional genomics of cucurbit crops

“…Moreover, several species such as pumpkin and bottle gourd have been used as rootstocks for other cucurbit crops in order to enhance tolerance to soil-borne diseases and abiotic stresses and to improve fruit yield and quality (2). Furthermore, the cucurbit species have long served as model systems for studies of fundamental biological processes such as fruit ripening (3), sex determination (4), and vascular development (5). In addition, both xylem and phloem sap of cucurbits can be readily collected for studies on long-distance signaling events (6).…”