Polygalacturonase: a candidate gene for the soft flesh and deciduous fruit mutation in Capsicum

The soft flesh and deciduous fruit of pepper (Capsicum spp.) originated from the wild C. frutescens BG 2816 accession is a complete dominant trait controlled by the S gene. We constructed an F2 population from a cross of BG 2816 (SS) and the bell-type C. annuum cultivar Maor (ss) and determined that S cosegregated with the tomato fruit-specific endo-polygalacturonase (PG) gene. The soft flesh and deciduous fruit phenotypes were observed together in all F2 individuals, indicating a pleiotropic effect of PG on the two traits. We mapped S to pepper chromosome 10 in the region corresponding to that in which PG was previously mapped in tomato. Northern, RT-PCR and western analyses and enzyme activity assays, collectively, indicated that PG is not detected in green, breaker or red fruits of Maor, nor in green fruits of BG 2816. Accumulation of PG mRNA and protein was detected in the fruits of BG 2816, and it increased during ripening from breaker to red stages. The sequence analysis of partial PG cDNA isolated from BG 2816 revealed high homology (87% identity) with the tomato PG. The resemblance of the soft flesh and deciduous fruit phenotypes to PG-associated phenotypes in other fruit crops, the complete linkage between S and PG, and the greater expression of PG in the fruits of BG 2816 than in those of Maor, all strongly indicate that PG is a candidate gene for S.