Abstract
Fruit abscission is triggered by multiple changes in endogenous components of the fruit, including energy metabolism. However, it is still unknown how the core energy metabolism pathways are modified during fruit abscission. Here, we investigated the relationship between carbon starvation-induced fruitlet abscission and energy metabolism changes in litchi. The fruitlet abscission of litchi ‘Feizixiao’ was induced sharply by girdling plus defoliation (GPD), a carbon stress treatment. Using liquid chromatography tandem mass spectrometry (LC-MS/MS) targeted metabolomics analysis, we identified a total of 21 metabolites involved in glycolysis, TCA cycle and oxidative phosphorylation pathways. Among them, the content of most metabolites in glycolysis pathways and TCA cycles was reduced, and the activity of corresponding metabolic enzymes such as ATP-dependent phosphofructokinase (ATP-PFK), pyruvate kinase (PK), citrate synthase (CS), succinate thiokinase (SAT), and NAD-dependent malate dehydrogenase (NAD-MDH) was decreased. Consistently, we further showed that the expression of the relative genes (LcPFK2, LcPK2, LcPK4, LcCS1, LcCS2, LcSAT, LcMDH1 and LcMDH2) was also significantly down-regulated. In contrast, the level of ATP, an important metabolite in the oxidative phosphorylation pathway, was elevated in parallel with both higher activity of H+-ATPase and the increased expression level of LcH+-ATPase1. In conclusion, our findings suggest that carbon starvation can induce fruitlet abscission in litchi probably by energy depletion that mediated through both the suppression of the glycolysis pathway and TCA cycle and the enhancement of the oxidative phosphorylation pathway.
Highlights
Litchi (Litchi chinensis Sonn.) is an important economic fruit crop widely grown inSouth China and Southeast Asia
Of control fruitlets dropped (Figure 1). These results indicate that girdling plus defoliation (GPD)-induced carbon starvation can activate litchi fruitlet abscission in a couple of days
These results indicate that oxidative phosphorylation pathway (OXPHOS) was enhanced in GPD-treated litchi fruitlitchi fruitlets
Summary
Litchi (Litchi chinensis Sonn.) is an important economic fruit crop widely grown in. South China and Southeast Asia. The energy metabolism of peach and banana under low temperature after harvest was deprived as the activity of H+ -ATPase, succinic dehydrogenase, and ATP content was decreased [12,13] These findings suggest that the energy metabolism pathways show different change patterns in response to different stress conditions. Genes related to EMP, such as those encoding pyruvate dehydrogenase and citrate synthase, were down-regulated in the process of litchi fruit abscission induced by carbon stress [19] These results imply that energy metabolism is altered during the process of fruit abscission caused by carbon stress. This study provides new insight into the multi-dimensional changes of energy metabolism pathways in carbon stress induced litchi fruitlet abscission, including gene expression, enzyme activity, and metabolite content
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