A SEPALLATA gene is involved in the development and ripening of strawberry (Fragaria x ananassa Duch.) fruit, a non-climacteric tissue

Abstract

Climacteric and non-climacteric fruits have traditionally been viewed as representing two distinct programmes of ripening associated with differential respiration and ethylene hormone effects. In climacteric fruits, such as tomato and banana, the ripening process is marked by increased respiration and is induced and co-ordinated by ethylene, while in non-climacteric fruits, such as strawberry and grape, it is controlled by an ethylene-independent process with little change in respiration rate. The two contrasting mechanisms, however, both lead to texture, colour, and flavour changes that probably reflect some common programmes of regulatory control. It has been shown that a SEPALLATA(SEP)4-like gene is necessary for normal ripening in tomato. It has been demonstrated here that silencing a fruit-related SEP1/2-like (FaMADS9) gene in strawberry leads to the inhibition of normal development and ripening in the petal, achene, and receptacle tissues. In addition, analysis of transcriptome profiles reveals pleiotropic effects of FaMADS9 on fruit development and ripening-related gene expression. It is concluded that SEP genes play a central role in the developmental regulation of ripening in both climacteric and non-climacteric fruits. These findings provide important information to extend the molecular control of ripening in a non-climacteric fruit beyond the limited genetic and cultural options currently available.

Fig. 1.

Phylogenetic analysis of SEPALLATA proteins in selected fruit species. A phylogenetic tree of full-length protein sequences from apple (Malus domestica), Arabidopsis, banana (Musa acuminata), grape (Vitis vinifera), papaya (Carica papaya), peach (Prunus persica), strawberry (Fragaria×ananassa), and tomato (Solanum lycopersicum) was constructed using MegAlign software (DNAStar) after aligning by ClustalW.

Fig. 2.

A MADS-box gene affects flower and fruit development in strawberry.(A) Altered development of flowers and fruit in untransformed (WT) strawberry and three independent lines (MADS A, MADS I, and MADS J) transformed with an antisense strawberry FaMADS9 transgene sequence. P, attached petals.(B) Anthers in two independent transformed lines (MADS A and MADS I).

Fig. 3.

Repression of strawberry FaMADS9 alters normal ripening.(A) Chlorophyll content in achenes; (B) anthocyanin content in receptacle tissue of three independent fruits sampled at each stage of development; (C) firmness of receptacle tissue. Measurements were made on 43, 35, and 30 ripe fruits from untransformed, MADS A and MADS I plants, respectively. Bars represent mean values (±SEM) of untransformed wild type (white) and independent antisense transformants MADS A (grey) and MADS I (black). SG and MG are small green and mature green fruits, respectively.

Fig. 4.

FaMADS9 gene expression in strawberry receptacles, achenes and petals.(A) Receptacle tissue; (B) achenes; (C) petals. Expression of an endogenous RIN-like gene was determined by absolute QRT-PCR. Bars indicate the mean values (±SEM) of three fruits sampled from each line (see Fig. 2) at different stages of development. Data for wild-type petals only extends to day 2 as from this point these petals abscised.

Fig. 5.

Expression of selected strawberry genes determined by absolute QRT-PCR. (A) SEP3-like MADS-box gene (DV440160); (B) SHATTERPROOF2-like MADS-box gene (CO380891); (C) endo-1,4-β-D-glucanase (AF041405); (D) AGL6-like MADS-box gene (DV440581); (E) AGAMOUS-like MADS-box gene (AF168468).Bars represent mean values (±SEM) of three fruits sampled from each line (see Fig. 2).

Fig. 6.

Expression of FaMADS4 in strawberry receptacle. Expression of a SEP4-like gene was determined by absolute QRT-PCR. Bars indicate the mean values (±SEM) of three fruits sampled from each line (see Fig. 2) at different stages of development.