Comparative transcriptome analysis reveals key genes potentially related to organic acid and sugar accumulation in loquat

Abstract

Organic acids and sugars are the primary components that determine the quality and flavor of loquat fruits. In the present study, major organic acids, sugar content, enzyme activities, and the expression of related genes were analyzed during fruit development in two loquat cultivars, ’JieFangZhong’ (JFZ) and ’BaiLi’ (BL). Our results showed that the sugar content increased during fruit development in the two cultivars; however, the organic acid content dramatically decreased in the later stages of fruit development. The differences in organic acid and sugar content between the two cultivars primarily occured in the late stage of fruit development and the related enzymes showed dynamic changes in activies during development. Phosphoenolpyruvate carboxylase (PEPC) and mNAD malic dehydrogenase (mNAD-MDH) showed higher activities in JFZ at 95 days after flowering (DAF) than in BL. However, NADP-dependent malic enzyme (NADP-ME) activity was the lowest at 95 DAF in both JFZ and BL with BL showing higher activity compared with JFZ. At 125 DAF, the activity of fructokinase (FRK) was significantly higher in JFZ than in BL. The activity of sucrose synthase (SUSY) in the sucrose cleavage direction (SS-C) was low at early stages of fruit development and increased at 125 DAF. SS-C activity was higher in JFZ than in BL. vAI and sucrose phosphate synthase (SPS) activities were similar in the two both cultivars and increased with fruit development. RNA-sequencing was performed to determine the candidate genes for organic acid and sugar metabolism. Our results showed that the differentially expressed genes (DEGs) with the greated fold changes in the later stages of fruit development between the two cultivars were phosphoenolpyruvate carboxylase 2 (PEPC2), mNAD-malate dehydrogenase (mNAD-MDH), cytosolic NADP-ME (cyNADP-ME2), aluminum-activated malate transporter (ALMT9), subunit A of vacuolar H+-ATPase (VHA-A), vacuolar H+-PPase (VHP1), NAD-sorbitol dehydrogenase (NAD-SDH), fructokinase (FK), sucrose synthase in sucrose cleavage (SS-C), sucrose-phosphate synthase 1 (SPS1), neutral invertase (NI), and vacuolar acid invertase (vAI). The expression of 12 key DEGs was validated by quantitative reverese transcription PCR (RT-qPCR). Our findings will help understand the molecular mechanism of organic acid and sugar formation in loquat, which will aid in breeding high-quality loquat cultivars.

Sugar and acid profile of loquat (Eriobotrya japonica Lindl.), enzymes assay and expression profiling of their metabolism-related genes as influenced by exogenously applied boron

“…Among them, the content of malic acid accounted for about 70%-80% of the total acid. These results are in line with the previous findings about organic acid profile of loquat ( 2009 ; Chen et al., 2007 ; Yang et al., 2021 ). The composition and content of organic acids in loquat fruits have genetic variation ( Famiani et al., 2015 ), and the differences are also manifested between different varieties ( Chen et al., 2009 ).…”

“…The composition and content of organic acids in loquat fruits have genetic variation ( Famiani et al., 2015 ), and the differences are also manifested between different varieties ( Chen et al., 2009 ). In present study, the cultivar “Jiefangzhong” was used as plant material which is already reported as high-acid cultivar ( Chen et al., 2007 ; 2009 ; Ali et al., 2021a ; Yang et al., 2021 ).…”

Postharvest Biology and Technology of Loquat (Eriobotrya japonica Lindl.)

“…However, sucrose accumulation is very high during the early fruit maturation phase and is also the predominant sugar in mature loquat fruit [ 2 ]. Similarly, glucose and fructose contents also increase with the advancement of loquat fruit maturation [ 7 ]. During ripening, the accumulation of sucrose by the metabolism of polysaccharide molecules is triggered by a series of sugar-metabolizing enzymes including sucrose phosphate synthase (SPS), sucrose synthase (SS), and acid invertase (AI), while the major enzymes catalyzing the metabolism of sorbitol in ripening loquat are sorbitol-6-phosphate dehydrogenase (S6PDH), sorbitol dehydrogenase (SDH), and sorbitol oxidase (SOX) [ 53 , 54 , 55 ].…”

“…The highest total phenolic contents (TPC) have been reported in ‘Mizauto’ fruit as compared to other cultivars [ 4 ]. Loquat fruit ripening is a complex process of different physiological and metabolic changes, mainly including: ethylene biosynthesis and respiratory modifications [ 5 ], colour modifications due to carotenoid biosynthesis [ 6 ], sugar and acid metabolism contributing to the variation in fruit sensory attributes [ 7 ] and changes in the lignin, polysaccharide, and pectin contents during fruit ripening resulting in cell wall modifications and fruit firmness changes during ripening [ 8 ]. These changes are associated with complex transcriptional elucidations and interlinked metabolic changes in loquat fruit.…”

An Updated Review on the Modulation of Carbon Partitioning and Allocation in Arbuscular Mycorrhizal Plants

“…Sucrose downloaded into the sink tissues can be the substrate for different metabolic pathways to generate energy or it can act as a C-skeleton to support the biosynthesis of structural molecules, reserve polymers, or specific metabolites in response to environmental conditions (Figure 1). The expression and enzymatic activity of the SPS gene have been observed in diverse non-photosynthetic organs such as germinating seedlings, leaves during the sink-to-source transition, and the pollen of immature inflorescences, where Suc biosynthesis and allocation also occur, to support the formation of polymeric compounds and the accumulation of carbohydrates in response to environmental stresses, including water deficits and extreme temperatures [63,[65][66][67][68][69][70][71].…”