Abstract
BackgroundDioecy is an important sexual system wherein, male and female flowers are borne on separate unisexual plants. Knowledge of sex-related differences can enhance our understanding in molecular and developmental processes leading to unisexual flower development. Coccinia grandis is a dioecious species belonging to Cucurbitaceae, a family well-known for diverse sexual forms. Male and female plants have 22A + XY and 22A + XX chromosomes, respectively. Previously, we have reported a gynomonoecious form (22A + XX) of C. grandis bearing morphologically hermaphrodite flowers (GyM-H) and female flowers (GyM-F). Also, we have showed that foliar spray of AgNO3 on female plant induces morphologically hermaphrodite bud development (Ag-H) despite the absence of Y-chromosome.ResultsTo identify sex-related differences, total proteomes from male, female, GyM-H and Ag-H flower buds at early and middle stages of development were analysed by label-free proteomics. Protein search against the cucumber protein sequences (Phytozome) as well as in silico translated C. grandis flower bud transcriptome database, resulted in the identification of 2426 and 3385 proteins (FDR ≤ 1%), respectively. The latter database was chosen for further analysis as it led to the detection of higher number of proteins. Identified proteins were annotated using BLAST2GO pipeline. SWATH-MS-based comparative abundance analysis between Female_Early_vs_Male_Early, Ag_Early_vs_Female_Early, GyM-H_Middle_vs_Male_Middle and Ag_Middle_vs_ Male_Middle led to the identification of 650, 1108, 905 and 805 differentially expressed proteins, respectively, at fold change ≥1.5 and P ≤ 0.05. Ethylene biosynthesis-related candidates as highlighted in protein interaction network were upregulated in female buds compared to male buds. AgNO3 treatment on female plant induced proteins related to pollen development in Ag-H buds. Additionally, a few proteins governing pollen germination and tube growth were highly enriched in male buds compared to Ag-H and GyM-H buds.ConclusionOverall, current proteomic analysis provides insights in the identification of key proteins governing dioecy and unisexual flower development in cucurbitaceae, the second largest horticultural family in terms of economic importance. Also, our results suggest that the ethylene-mediated stamen inhibition might be conserved in dioecious C. grandis similar to its monoecious cucurbit relatives. Further, male-biased proteins associated with pollen germination and tube growth identified here can help in understanding pollen fertility.
Highlights
Dioecy is an important sexual system wherein, male and female flowers are borne on separate unisexual plants
Protein identification using Cucumis sativus protein sequences as database led to the identification of 2426 proteins, out of which 434 were new proteins that were not detected using the in silico translated in-house C. grandis flower bud transcriptome (Additional file 1: Data S1)
All the following analyses were carried out using C. grandis transcriptome as the database, since it led to the detection of a higher number of proteins
Summary
Dioecy is an important sexual system wherein, male and female flowers are borne on separate unisexual plants. Around 90% of the angiosperm species are hermaphroditic bearing perfect flowers having both male as well as female reproductive sex organs [1]. Remaining ~ 5% angiosperm species are dioecious, having separate unisexual plants bearing either only male or female flowers [2,3,4]. Dioecious species show patchy phylogenetic distribution and are reported in around three-fourth of the angiosperm families. This indicates that the evolution of dioecy has occurred multiple times in different families independently and the molecular mechanisms of sex determination might vary between distant dioecious species and is a matter of great research interest [5,6,7]. The mechanism of sex determination in plants can be complex and it may involve environmental factors apart from genetic factors [9]
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