Functional Characterization of SlSAHH2 in Tomato Fruit Ripening.

Lu Yang,Sidra Habib,Guojian Hu,Ning Li,Wei Huang,Zhengguo Li

doi:10.3389/fpls.2017.01312

Abstract

S-adenosylhomocysteine hydrolase (SAHH) functions as an enzyme catalyzing the reversible hydrolysis of S-adenosylhomocysteine to homocysteine and adenosine. In the present work we have investigated its role in the ripening process of tomato fruit. Among the three SlSAHH genes we demonstrated that SlSAHH2 was highly accumulated during fruit ripening and strongly responded to ethylene treatment. Over-expression of SlSAHH2 enhanced SAHH enzymatic activity in tomato fruit development and ripening stages and resulted in a major phenotypic change of reduced ripening time from anthesis to breaker. Consistent with this, the content of lycopene was higher in SlSAHH2 over-expression lines than in wild-type at the same developmental stage. The expression of two ethylene inducible genes (E4 and E8) and three ethylene biosynthesis genes (SlACO1, SlACO3 and SlACS2) increased to a higher level in SlSAHH2 over-expression lines at breaker stage, and one transgenic line even produced much more ethylene than wild-type. Although inconsistency in gene expression and ethylene production existed between the two transgenic lines, the transcriptional changes of several important ripening regulators such as RIN, AP2a, TAGL1, CNR and NOR showed a consistent pattern. It was speculated that the influence of SlSAHH2 on ethylene production was downstream of the regulation of SlSAHH2 on these ripening regulator genes. The over-expressing lines displayed higher sensitivity to ethylene in both fruit and non-fruit tissues. Ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) treatment accelerated ripening faster in SlSAHH2 over-expressing fruit than in wild-type. Additionally, seedlings of transgenic lines displayed shorter hypocotyls and roots in ethylene triple response assay. In conclusion, SlSAHH2 played an important role in tomato fruit ripening.

Highlights

Tomato (Solanum lycopersicum L.) is one of the most important horticultural crops supplying vitamins and nutrition for human throughout the world
These results indicated that the expression patterns of the three SlSAHH genes were all different and SlSAHH2 may function in the process of fruit ripening
The results suggested that over-expression of SlSAHH2 in tomato influenced the expression of ripening regulators and ethylene related genes significantly, which even enhanced ethylene production

Summary

Introduction

Tomato (Solanum lycopersicum L.) is one of the most important horticultural crops supplying vitamins and nutrition for human throughout the world. Color, texture, flavor as well as nutritional status of fruit change and seeds are dispersed (Prasanna et al, 2007; Rugkong et al, 2011). SlSAHH2 Impacts Tomato Fruit Ripening has been classified as climacteric fruit, showing increased ethylene production at or just before the onset of ripening and requiring ethylene to complete the ripening process (Alexander and Grierson, 2002; Paul et al, 2012). S-adenosylmethionine (SAM) is the substrate; 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) and ACC oxidase (ACO) are two rate-limiting enzymes (Adams and Yang, 1979; Prasanna et al, 2007). Tomato fruit color changes by degradation of chlorophyll and accumulation of carotenoids during ripening. Lycopene is one of the major carotenoids providing red color for tomato fruit (Ronen et al, 1999)

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Results

Conclusion