The regulation of MADS-box gene expression during ripening of banana and their regulatory interaction with ethylene

Abstract

Six MaMADS-box genes have been cloned from the banana fruit cultivar Grand Nain. The similarity of these genes to tomato LeRIN is low and neither MaMADS2 nor MaMADS1 complement the tomato rin mutation. Nevertheless, the expression patterns, specifically in fruit and the induction during ripening and in response to ethylene and 1-MCP, suggest that some of these genes may participate in ripening. MaMADS1, 2, and 3, are highly expressed in fruit only, while the others are expressed in fruit as well as in other organs. Moreover, the suites of MaMADS-box genes and their temporal expression differ in peel and pulp during ripening. In the pulp, the increase in MaMADS2, 3, 4, and 5 expression preceded an increase in ethylene production, but coincides with the CO2 peak. However, MaMADS1 expression in pulp coincided with ethylene production, but a massive increase in its expression occurred late during ripening, together with a second wave in the expression of MaMADS2, 3, and 4. In the peel, on the other hand, an increase in expression of MaMADS1, 3, and to a lesser degree also of MaMADS4 and 2 coincided with an increase in ethylene production. Except MaMADS3, which was induced by ethylene in pulp and peel, only MaMADS4, and 5 in pulp and MaMADS1 in peel were induced by ethylene. 1-MCP applied at the onset of the increase in ethylene production, increased the levels of MaMADS4 and MaMADS1 in pulp, while it decreased MaMADS1, 3, 4, and 5 in peel, suggesting that MaMADS4 and MaMADS1 are negatively controlled by ethylene at the onset of ethylene production only in pulp. Only MaMADS2 is neither induced by ethylene nor by 1-MCP, and it is expressed mainly in pulp. Our results suggest that two independent ripening programs are employed in pulp and peel which involve the activation of mainly MaMADS2, 4, and 5 and later on also MaMADS1 in pulp, and mainly MaMADS1, and 3 in peel. Hence, our results are consistent with MaMADS2, a SEP3 homologue, acting in the pulp upstream of the increase in ethylene production similarly to LeMADS-RIN.

Banana MaMADS Transcription Factors Are Necessary for Fruit Ripening and Molecular Tools to Promote Shelf-Life and Food Security

“…S2). MaMADS2 and MaMADS1 are most similar to SlMADS-RIN, with 62% and 56% amino acid identity, respectively (Elitzur et al, 2010).…”

“…S1), indicating that ripening is initiated in the pulp. We previously described the expression of six MaMADS box genes from banana fruit (Elitzur et al, 2010), and based on RNA sequencing (RNAseq) data, we discovered seven additional highly expressed MaMADS box genes (more than 50 reads per kilobase of transcript per million reads mapped [RPKM]) in the pulp of banana. Homologs of SlFUL1/2, SlTAGL1, and SlMADS-RIN were identified and used to construct a phylogenetic tree (Supplemental Fig.…”

“…These MaMADS box genes contain four domains: M, I, K, and C, with the M domain most conserved. The C region is the most divergent, as is typical of MADS box genes (Elitzur et al, 2010); therefore, all three repression constructs targeted the C region (Supplemental Fig. S3).…”

“…MaMADS1 to MaMADS4 may function similarly to RIN in tomato, being SEP genes (Elitzur et al, 2010), and MaMADS5 may function like TAGL1, being an AG gene (Itkin et al, 2009;Vrebalov et al, 2009). MaMADS5 was found to bind to CArG box sequences, which exist in the promoters of major ripening genes (Choudhury et al, 2012) and recently was found to bind to OVATE FAMILY PROTEIN (Liu et al, 2015b), a suppressors of cell elongation (Wang et al, 2007).…”

“…The expression of the MaMADS1 to MaMADS5 genes was induced during ripening with gene-specific variation in the pulp and peel, with MaMADS1 most highly ripening induced. Some of these genes were ethylene inducible in peel and/or pulp, but MaMADS2 was not induced by ethylene in either (Elitzur et al, 2010; http://bananagenome.cirad.fr/cgi-bin/gbrowse/musa_acuminata/? name=GSMUA_Achr1P12150_001).…”