The ripening of fleshy fruits is a complex, genetically programmed process that impacts fruit nutritional quality and shelf life. Based on the different ripening mechanisms, fruits are classified into two groups: climacteric (e.g. tomato, apple and banana) and non-climacteric (e.g. strawberry, grape, and citrus). Phytohormone ethylene is essential for the ripening of climacteric fruits, while the ripening of non-climacteric fruits is thought to be abscisic acid (ABA)-dependent.
A research group from the Institute of Botany of the Chinese Academy of Sciences (IBCAS) has shown that mRNA m6A methylation, which is considered as an mRNA "epitranscriptome", participates in the ripening control of climacteric fruit tomato. However, whether m6A is evolutionarily conserved among different types of fruits has not been defined. Moreover, the regulatory function of m6A in ripening of non-climacteric fruits remains elusive.
In a study published in Genome Biology, the same group led by Dr. QIN Guozheng from IBCAS demonstrated that m6A methylation regulates the ripening of strawberry, a classical non-climacteric fruit, by targeting ABA pathway.
The researchers found that m6A methylation displays a dramatic change at ripening onset of strawberry. The m6A modification in the coding sequence regions appears to be ripening-specific and tends to stabilize the mRNAs, whereas m6A around the stop codons and within the 3' untranslated regions is generally negatively correlated with the abundance of the mRNAs.
They identified thousands of transcripts with m6A hypermethylation in the coding sequence regions, including those of NCED5, ABAR, and AREB1 in the ABA biosynthesis and signaling pathway.
Further analysis demonstrated that the methyltransferases MTA and MTB are indispensable for normal ripening of strawberry fruit, and MTA-mediated m6A modification promotes mRNA stability of NCED5 and AREB1, while facilitates translation of ABAR.
"This work reveals a regulatory role of m6A methylation on the ripening of the non-climacteric strawberry fruit. These findings provide new insights into understanding the regulatory networks controlling fruit ripening," said Prof. QIN Guozheng.
This study was funded by the National Key Research and Development Program of China and the National Natural Science Foundation of China.
Representative images of octoploid cultivated strawberry fruit at various developmental stages (Image by IBCAS)
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