Transcriptome and Metabolome Analysis Provide New Insights into the Process of Tuberization of Sechium edule Roots

Abstract

Chayote (Sechium edule) produces edible tubers with high starch content after 1 year of growth but the mechanism of chayote tuberization remains unknown. ‘Tuershao’, a chayote cultivar lacking edible fruits but showing higher tuber yield than traditional chayote cultivars, was used to study tuber formation through integrative analysis of the metabolome and transcriptome profiles at three tuber-growth stages. Starch biosynthesis- and galactose metabolism-related genes and metabolites were significantly upregulated during tuber bulking, whereas genes encoding sugars will eventually be exported transporter (SWEET) and sugar transporter (SUT) were highly expressed during tuber formation. Auxin precursor (indole-3-acetamide) and ethylene precursor, 1-aminocyclopropane-1-carboxylic acid, were upregulated, suggesting that both hormones play pivotal roles in tuber development and maturation. Our data revealed a similar tuber-formation signaling pathway in chayote as in potatoes, including complexes BEL1/KNOX and SP6A/14-3-3/FDL. Down-regulation of the BEL1/KNOX complex and upregulation of 14-3-3 protein implied that these two complexes might have distinct functions in tuber formation. Finally, gene expression and microscopic analysis indicated active cell division during the initial stages of tuber formation. Altogether, the integration of transcriptome and metabolome analyses unraveled an overall molecular network of chayote tuberization that might facilitate its utilization.

Genome-Wide Identification of the MADS-Box Gene Family during Male and Female Flower Development in Chayote (Sechium edule)

“…The expression data of ‘Tuershao’ root tubers of three different developmental stages (T1: early, T2: middle, and T3: mature stages) were obtained from our previous transcriptome data [ 22 ]. Briefly, the FPKM value of the MADS gene in transcriptome data was log2 standardized and displayed by heat map [ 47 ].…”

“…The female flower of ‘Tuershao’ cannot expand into fruit normally, as with the chayote. The edible root tuber in the underground is its main product, and the root tuber yield is much higher than that of chayote [ 22 ]. For the tissue-specific expression analysis, we collected the roots, stems, leaves, tendrils, and open male and female flowers of ‘Tuershao’ and chayote; for floral organ development expression analysis, the male and female flower samples of ‘Tuershao’ and chayote with different diameters were collected and named S1 to S5, then immediately frozen in liquid nitrogen and stored at −80 °C.…”

“…The qRT-PCR was performed on a Bio-Rad CFX96 Real-Time System with 2X SYBR Green Abstart PCR Mix (Sangon Biotech, Beijing, China). The chayote actin gene was used as the internal reference and the relative expression levels of each MADS gene was calculated using the 2 −∆∆Ct method [ 22 ]. All of the primers used for qRT-PCR are shown in Table S4 .…”

“…From May to July, only male flowers generally open. From September to November, the female flowers will bear fruit; the chayote tuber only blooms from September to November every year, and its female flower cannot normally expand into fruit [ 22 ]. Compared with Cucurbitaceae crops such as cucumber, melon, pumpkin and watermelon, the research on chayote is relatively sparse.…”

Physiological, anatomical and quality indexes of root tuber formation and development in chayote (Sechium edule)

“…Previous reports have suggested that the formation of root tuber may be due to higher growth vigor and excessive assimilates flowing to the root to withstand adverse growth conditions [ 8 ]. Our previous research has also confirmed that the formation of root tubers is accompanied by upregulation of starch genes and changes in sugar transporters [ 9 ]. Moreover, the nutrient-rich root tuber is being studied in depth.…”