Assessing the allelotypic effect of two aminocyclopropane carboxylic acid synthase-encoding genes MdACS1 and MdACS3a on fruit ethylene production and softening in Malus

• Published in: Horticulture research 2016-05, Vol.3 (1), p.16024-16024, Article 16024
• Main Authors: Dougherty, Laura, Zhu, Yuandi, Xu, Kenong
• Format: Article
• Language: English
• Subjects: 631/449/1870; 631/449/711; Agriculture; Biomedical and Life Sciences; Ecology; Life Sciences; Plant Breeding/Biotechnology; Plant Genetics and Genomics; Plant Sciences
• ISSN: 2052-7276; 2052-7276
• DOI: 10.1038/hortres.2016.24

Phytohormone ethylene largely determines apple fruit shelf life and storability. Previous studies demonstrated that MdACS1 and MdACS3a , which encode 1-aminocyclopropane-1-carboxylic acid synthases (ACS), are crucial in apple fruit ethylene production. MdACS1 is well-known to be intimately involved in the climacteric ethylene burst in fruit ripening, while MdACS3a has been regarded a main regulator for ethylene production transition from system 1 (during fruit development) to system 2 (during fruit ripening). However, MdACS3a was also shown to have limited roles in initiating the ripening process lately. To better assess their roles, fruit ethylene production and softening were evaluated at five time points during a 20-day post-harvest period in 97 Malus accessions and in 34 progeny from 2 controlled crosses. Allelotyping was accomplished using an existing marker (ACS1) for MdACS1 and two markers (CAPS 866 and CAPS 870 ) developed here to specifically detect the two null alleles ( ACS3a-G289V and Mdacs3a ) of MdACS3a . In total, 952 Malus accessions were allelotyped with the three markers. The major findings included: The effect of MdACS1 was significant on fruit ethylene production and softening while that of MdACS3a was less detectable; allele MdACS1–2 was significantly associated with low ethylene and slow softening; under the same background of the MdACS1 allelotypes, null allele Mdacs3a (not ACS3a-G289V ) could confer a significant delay of ethylene peak; alleles MdACS1–2 and Mdacs3a (excluding ACS3a-G289V ) were highly enriched in M. domestica and M. hybrid when compared with those in M. sieversii . These findings are of practical implications in developing apples of low and delayed ethylene profiles by utilizing the beneficial alleles MdACS1-2 and Mdacs3a . Apple storage: Mutations make for slower softening Years of conventional breeding have increased the frequency of two gene mutations promoting slower ripening and longer shelf life in apples. Researchers at Cornell University, USA, led by Kenong Xu, studied two genes with major roles in producing ethylene in apples. Ethylene, a plant hormone, is a key player in fruit ripening and softening. They identified mutated forms (‘alleles’) of both genes which caused lower ethylene production, slower ripening, and better fruit storage properties. Comparing the frequency of different alleles across apple species, Xu's team found that low-ethylene alleles were much more prevalent in two varieties of cultiva