In this article we will discuss about the controlling of fruit ripening in banana, water melon and apple.
Extended Longevity of Banana Fruit:
Banana is a staple food for nearly more than 450 million people particularly from developing world. They are ranked second in the world next to grapes. Banana is a climacteric fruit as tomatoes. Therefore, it is possible to extend longivity of banana fruit using antisense inhibition of ethylene production.
The characteristics of banana (Musa accuminata) genes encoding ACC synthase and ACC oxidase was identified by constructing cDNA library using mRNA of ripening banana fruit.
The PCR products were screened in the library and cloned cDNA insert for ACC oxidase referred as BACS, was 1231 bp long (ORF) which encodes for 315 amino acid length enzyme. In another study, a cDNA clones, designed as MaACS encoding ACC synthase was isolated by screening cDNA library. The sequence analysis revealed that MaACS (BACS) was 1675 bp/long and contained one open reading frame encoding a single polypeptide of 486 amino acids.
The amino acid sequence of this gene exhibit well conserved domain of ACC synthase gene and resembles most of the tomato (Lycopersecun esculentum) ACC synthase gene (ACS-A) with 62% homology. Differential expression of enzyme activity at different stages of fruit development was noticed in banana.
For example, transcript accumulation was comparatively high in fruit peel than in the pulp of ripening fruit. This differential longevity shows that ethylene produced during fruit ripening was mainly from peel. Except BaC53, which is expressed only in ripening fruit, two more genes of ACC synthase sequences of about 1.4 kb designed as BaCS1 and BaCS2 expressed only in green peel and young leaf?
Control of Softening in Water Melon:
Water melon is also a typical climacteric fruit and there is sharp increase in ethylene control during ripening stage that is acceptable for eating. Presently most of the antisense mediated manipulation is confined only to tomato fruits. Melon is less attractive model plant for manipulation due to its extensive chromosome map and lack of mutants. In addition, fruits are difficult to obtain in winter and are restricted to two or three per plant.
However, melon of Cantalope charentais type represents valuable target for improved shelf life. Through genetic manipulation and also its unique organoleptic characters such as accumulation of large sum of sugar etc. Melon transformation was carried out using cotyledon explants and was cocultivated with engineered binary vector of harbouring an antisense construct of ACC oxidase and marker gene like NPT II.
Transgenic melon exhibiting a sharp reduction in ethylene production and significant inhibition of fruit ripening has been generated. Studies with Cantalope charentais displayed a higher internal ethylene concentration than other melon varieties and much higher than tomato.
Control of Softening in Apple:
Apples are important nutritional potential crop in the world with an annual production of USA alone exceeds 5 million tonnes as one of the largest application in USA. Mc Intosh apple characterized by its pleasant aroma, deep red colour and its exemplary firm texture.
However, short life span of Mcintosh apple particularly after its harvest posess serious concerns in view of its economic potential. Although several conventional methods in controlled storage using gas composition and temperature is under controlled conditions, extended life span not goes beyond 4 month using antisense RNA technology.
1093 bp ACC synthase gene isolated from apple and tomato was inserted in reverse orientation between the CaMV-35S promoter and the Kanamycin resistance marker gene and transformation was achieved using efficient vector.
Transgenic Mcintosh apple tree soften slower than normal plant fruit, thereby extending shelf life of apple. Implementation of antisense RNA results in better fruit quality, longer shelf life and easy for transportation.