Shelf Life Regulator-Polyamines

Kexin Wang, Purdue University

Abstract

Shelf life of ripe tomato fruit is economically very important, it determines the cash returns to the grower and the grocer/processor from the production to the marketing chain. Shelf life of horticultural edible produce is regulated through myriad physiological, biochemical and environmental processes. Tomato is climacteric fruit, which undergoes increases in respiration and ethylene production at the onset of ripening. Tomato fruit ripening is associated with marked changes in gene expression, biosynthesis of a large number of catabolic enzymes, including cell wall hydrolases implicated in fruit softening. Ripening-associated changes in sugars, acids and volatile compounds determine the organoleptic characteristics. Ripening-impaired tomato mutants and genetically engineered genotypes have longer shelf life, but fruits from a majority of these cultivars are generally of low quality. Postharvest management technology in Chapter 1, including modified atmosphere packaging, temperature and humidity control, provide efficient control in extending fruit shelf life. Chapter I also summarized the advance in genetically regulating fruit ripening. Such information is expected to contribute to devising new methods to prolong tomato fruit shelf life. PAs are important molecular in living organisms. We determined the effect of higher Spd/Spm on transcriptome during ripening in transgenic tomato overexpressing ySAMDC gene under SlE8 promoter by using RNA-Seq method and DEG analysis. PAs regulated fruit ripening and extended tomato shelf life by changing the number of transcript of ripening-related genes. Function of DEG (the over 4000 differentially expressed genes) included methylation/demethylation, cell wall/membrane degradation, ethylene biosynthesis/signalling and ripening mutant genes, which are closely related to tomato fruit ripening and shelf life. PAs are not only involved in metabolic and catalytic activities but also nucleic acid binding and structure. The decrease in the expression of several genes regulating cell wall degradation and ripening positive regulators is consistent with the phenotype of high Spd/Spm tomato fruit that exhibit improved longer shelf life. Our results show that Put, Spd and Spm exert differential effects on ripening associated genes that can be divided into several clades including those exclusively affected by Put, Spd or Spm and those affected by more than one PAs. These results show that each PAs has distinct function. Transcripts of hormone biosynthesis and signaling were changed by higher Spd and Spm levels (and lower Put level) during ripening. Higher levels of PAs in 556HO (expressing yeast SAMDC in fruit by E8 promoter) enhanced ethylene production in tomato fruit by increasing the mRNA expression of ACSs and ACOs, especially at early ripening stage. Furthermore, Ethylene-responsive transcription factors (ERFs) were significantly up-regulated during fruit ripening. Auxin biosynthesis and signaling were promoted in 556HO fruit, especially at the later stage (B8) of ripening. GA biosynthesis gene and ABA signaling were inhibited. JA, SA, GA, CK and Brassinosteroids signaling genes were promoted in 556HO fruit. Gene expression related to JA and CK biosynthesis didn’t show consistent regulation pattern in 556HO. However, the correlation between gene expression and PAs levels in 556HO was complex.

Degree

Ph.D.

Advisors

Handa, Purdue University.

Subject Area

Molecular chemistry|Horticulture|Molecular physics

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