MicroRNAs and Transcripts Associated with an Early Ripening Mutant of Pomelo (Citrus grandis Osbeck)

Abstract

‘Liuyuezaoyou’ is an early-ripening cultivar selected from a bud mutation of Citrus grandis Osbeck ‘Guanximiyou’. They were designated here as MT and WT, respectively. The fruit of MT matures about 45 days earlier than WT, which was accompanied by significant changes in key phytohormones, sugar compounds and organic acids. Recent studies have showed that microRNAs (miRNAs) play an important role in regulation of fruit ripening process. The aim of this study was to compare MT fruits with WT ones to uncover if miRNAs were implicated in the ripening of C. grandis. Fruits of both WT and MT at four developmental stages were analyzed using high-throughput sequencing and RT-PCR. Several independent miRNA libraries were constructed and sequenced. A total of 747 known miRNAs were identified and 99 novel miRNAs were predicted across all libraries. The novel miRNAs were found to have hairpin structures and possess star sequences. These results showed that transcriptome and miRNAs are substantially involved in a complex and comprehensive network in regulation of fruit ripening of this species. Further analysis of the network model revealed intricate interactions of miRNAs with mRNAs during the fleshy fruit ripening process. Several identified miRNAs have potential targets. These include auxin-responsive protein IAA9, sucrose synthase 3, V-type proton ATPase, NCED1 (ABA biosynthesis) and PL1/5 (pectate lyase genes), as well as NAC100 putative coordinated regulation networks, whose interactions with respective miRNAs may contribute significantly to fruit ripening of C. grandis.

Comparative Transcriptome and sRNAome Analyses Reveal the Regulatory Mechanisms of Fruit Ripening in a Spontaneous Early-Ripening Navel Orange Mutant and Its Wild Type

“…As shown in Figure 4 , α-glucosidase and β-fructofuranosidase, which are key enzymes in fructose synthesis in the starch and sugar metabolism pathways, had higher expression levels in MT than WT, and these two genes were found to be upregulated to promote fructose accumulation in our previous research. This result is consistent with the pattern of expression of sugar components in the early-ripening mutant of the pomelo variety [ 51 ]. PG and PE are key genes regulating fruit ripening and softening [ 52 ].…”

Identification of Late Ripening Citrus Mutant, Ara-unshiu (Citrus unshiu), and Its Selectable Marker

“…Tardivo, another late-ripening mutant of the Clementine mandarin, is associated with an altered perception and sensitivity to ethylene [22]. Conversely, the Liuyuezaoyou mutant is an early-ripening cultivar selected from a bud mutation of Guanximiyou (Citrus grandis Osbeck) [23]. The Ganqi 4 mutant was also reported as a spontaneous early-ripening navel orange mutant of Newhall (Citrus sinensis L. Osbeck) [24].…”

“…The Ganqi 4 mutant was also reported as a spontaneous early-ripening navel orange mutant of Newhall (Citrus sinensis L. Osbeck) [24]. Tomato, strawberry, and pomelo mutants with altered timing of fruit ripening were also recently reported [23,[25][26][27]. To further characterize the process of fruit ripening, we investigated the morphological traits and sugar/acid contents of the late-ripening mutant Ara-unshiu.…”

Volatiles Accumulation during Young Pomelo (Citrus maxima (Burm.) Merr.) Fruits Development

“…During the development of young pomelo fruits, the relative fiber content was correspondingly decreased with the reduced proportion of peel, hence MYB108 down-regulated. Besides, Cg6g025130 ( NAC100 in Citrus clementina ) was putatively involved in regulation networks to contribute in fruit ripening of pomelos ( Citrus grandis Osbeck ) [ 34 ]. Hence the components correlated to Cyan Module could be used in discriminating young pomelo fruits at different developing stages.…”