Candidate genes transcriptional study in ‘Granny Smith’ apples in response to prolonged storage at different conservation strategies
Populin Francesca1 , Vittani Lorenzo1-2 , Nicola Busatto1, Stefan Stuerz3, Zanella Angelo3 and Costa Fabrizio2
Background - Apple (Malus domestica) is one of the most cultivated fruit crop worldwide (86 442 716 tons, FAOSTAT 2020) characterized by a mid-late summer harvesting To satisfy the continue demand of fresh product ensuring a constant availability on the market, fruit must be stored for prolonged period Nowadays this is facilitated by the employment of modern storage technologies based on low temperatures (14°C), slowing down the entire metabolisms, and the inhibition of the ripening process The control of the ripening syndrome can be also achieved through a controlled atmosphere characterized by a low-oxygen and high CO2 content, inhibiting the biosynthesis of the hormone ethylene, and/or treatment with the ethylene competitor 1-MCP that acting at the perception level efficiently block the hormonal signal transduction pathway
Experimental Goals – With the aims to improve and optimize the storage strategy reducing the quality loss and avoiding and/or limiting the onset of related post-harvest disorders, a deep understanding of how these storage conditions affect the ripening process and the quality of apples becomes essential
Material and Methods - In this study, different batches of ‘Granny Smith’ apple fruit were stored in various storage conditions, such as: Dynamic-Controlled-Atmosphere (DCA) and classical RegularAtmosphere (RA), with and without application of 1-MCP. After six months, apples were transferred at room temperature for seven days simulating a commercial shelf-life (SL) as illustrated in Figure 1
The postharvest ripening physiology was assessed by analyzing the transcriptional pattern of candidate genes involved in ethylene biosynthesis and ripening (ACO1, ACS1 and PG1), signal transduction pathway in response to low-oxygen (ERF-VIIs), sugars and anaerobic metabolisms (β-amylase-AMY , glucose-6-Pisomerase-GPI, pyruvate dehydrogenase-PDC and alcohol dehydrogenase-ADH) trough a RT-qPCR approach
Figure 2 - A) PCA performed on the expression profile of the genes used in this study B) Heatmap and clustering of the expression profile of the genes tested Three main clusters were highlighted with different colors PCO=plant cysteine oxidase; PFP=PPi-dependent phosphofructokinase; S6PDH=sorbitolo-6 phosphate dehydrogenase; INV=invertase; ERF=ethylene responsive factor; ALD=aldolase; ADH=alcohol dehydrogenase; ARF4=auxin responsive factor 4; GPI=glucose-6-Pisomerase; ENO=enolase; PDC=pyruvate decarboxylase; ACO=ACC oxidase; PPO=polyphenol oxidase; B_AMY=β-amylase; ERS=ethylene response sensor; AFS1=alpha farnesene synthase1; ACS=ACC synthase1; PG1=polygalacturonase1
Figure 3 - Expression profiles of selected genes representative of each cluster shown in Figure 2B. A) Alcohol Dehydrogenase – ADH B) Polyphenol Oxidase – PPO C) ACC synthase –ACS The colors of each rectangle in the panel correspond to the belonging cluster
Results – The PCA shown in Figure 2A highlight as the two PCs explain 81% of the total variability observed and distinguished the samples over the 2D plot base on the length of storage 6M (+) or 7dSL (-) The PCA well divided the samples stored in DCA or treated with 1-MCP from the RA samples This is also clearly illustrated in the Heatmap presented in Figure 2B where three main cluster were identified The yellow cluster is composed by the genes that shown a higher expression level during the storage period of 6M, especially in the DCA samples, as i e the alcohol dehydrogenase (Figure 3A) In the second one (orange) are grouped the genes that are accumulated in the RA samples such as the PPO (Figure 3B) Whereas the last cluster (blue) are represented by genes that are re-activated after the storage period, during the post-storage shelf-life ripening, especially in the DCA samples, both CTRL or 1-MCP treated (Figure 3C)
Conclusion - The transcriptional profiles of these candidate genes provides preliminary results about the physiological behavior of the fruit stored at different atmospheric conditions
1) Research and Innovation Centre, Fondazione Edmund Mach, Italy; 2) Center Agriculture Food Environment C3A, University of Trento, Italy; 3) Laimburg Research Centre for Agriculture and Forestry, Italy