Abstract
BackgroundRipening affects the quality and nutritional contents of fleshy fruits and is a crucial process of fruit development. Although several studies have suggested that ubiquitin-conjugating enzyme (E2s or UBC enzymes) are involved in the regulation of fruit ripening, little is known about the function of E2s in papaya (Carica papaya).Methodology/Principal findingsIn the present study, we searched the papaya genome and identified 34 putative UBC genes, which were clustered into 17 phylogenetic subgroups. We also analyzed the nucleotide sequences of the papaya UBC (CpUBC) genes and found that both exon-intron junctions and sequence motifs were highly conserved among the phylogenetic subgroups. Using real-time PCR analysis, we also found that all the CpUBC genes were expressed in roots, stems, leaves, male and female flowers, and mature fruit, although the expression of some of the genes was increased or decreased in one or several specific organs. We also found that the expression of 13 and two CpUBC genes were incresesd or decreased during one and two ripening stages, respectively. Expression analyses indicates possible E2s playing a more significant role in fruit ripening for further studies.ConclusionsTo the best of our knowledge, this is the first reported genome-wide analysis of the papaya UBC gene family, and the results will facilitate further investigation of the roles of UBC genes in fruit ripening and will aide in the functional validation of UBC genes in papaya.
Highlights
Papaya (Carica papaya) is an economically important fruit crop that is widely grown in tropical and sub-tropical regions, and its fleshy fruits play an important role in the human food supply, as well as in human nutrition and health [1, 2]
Several studies have suggested that ubiquitin-conjugating enzyme (E2s or UBC enzymes) are involved in the regulation of fruit ripening, little is known about the function of E2s in papaya (Carica papaya)
The ripening-associated genes that have been reported in tomato include: rin, which encodes a MADS-box transcription factor [13]; Nr, which encodes an ethylene receptor [14]; Cnr (Colorless nonripening), which encodes an SBP-box transcription factor [15]; Gr (Green ripe), which encodes a still poorly defined component of the ethylene transduction pathway [6]; SINAC4, a new tomato NAC transcription factor that positively regulates fruit ripening and carotenoid accumulation [16]; APETALA2a (AP2a), a transcription factor that regulates fruit ripening via regulation of ethylene biosynthesis and signaling [17]; LeNCED1, which initiates abscisic acid (ABA) biosynthesis at the onset of fruit ripening and might act as an original inducer in tomato [18]; and the tomato genes SHATTERPROOF, TAGL1 [19], TDR4/FUL1, and MBP7/FUL2 [20], which are involved in regulating fruit ripening
Summary
Papaya (Carica papaya) is an economically important fruit crop that is widely grown in tropical and sub-tropical regions, and its fleshy fruits play an important role in the human food supply, as well as in human nutrition and health [1, 2]. Fruit with different ripening mechanisms can be divided into two groups: climacteric fruit (e.g., bananas, tomatoes, pears, mangos, and papayas), in which ripening is accompanied by a peak in respiration and a concomitant burst of ethylene, and non-climacteric fruit (e.g., pineapple, carambola, borojo, and watermelon), in which respiration exhibits no dramatic change and ethylene production remains at a very low level [5]. In particular, has been extensively studied, owing to its crucial role in the ripening of climacteric fruits [6,7,8,9], and the biosynthesis, perception, and signal transduction of ethylene, as well as downstream gene regulation, are well known [10]. Several studies have suggested that ubiquitin-conjugating enzyme (E2s or UBC enzymes) are involved in the regulation of fruit ripening, little is known about the function of E2s in papaya (Carica papaya)
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