Executive summary

Objectives:

1. To identify and clone the SUPPRESSOR OF CONSTANS 1 (SOC1) gene from mangosteen.
2. To develop a technology for transformation and regeneration of mangosteen.
3. To transform mangosteen with SOC1 gene.

Mangosteen (Garcinia mangostana L.), well known as queen of the fruits, is the flagship fruit of Malaysia. It is exported to Singapore, Hong Kong and East Asia where Singapore was the main importer of Malaysian mangosteen in 1991-1997 1.

To spur on and expand the mangosteen fruit industry to one that is economically viable in Malaysia, much has to be done to address the problems associated with the industry. The planting of mangosteen is not done on a large scale due to its low fruit yield, biennial bearing, long juvenile period and high percentage of unmarketable fruit. Mangosteen is a seasonal crop which flowers and fruits between June and August. In certain year, there is a minor season towards the end of the year. This makes the marketing of mangosteen difficult due to inconsistency of fruit supply 2. Mangosteen trees are usually large and large trees take several years before they come into bearing which leads to the increment of overall cost of production per unit area 3. Beside the long juvenile period, mangosteen cultivation has also been hindered by low yield during early years of production. In addition, fruit size is highly variable with high proportion of small unmarketable fruit 4.

Through the advancement of gene technology, transferring of early flowering gene into mangosteen could help to solve its long juvenile period. Flowering time is a quantitative trait under the control of numerous genes. The genetic control of flowering time has been well studied in the plant model system Arabidopsis thaliana, where many of the genes involved have been cloned and characterised 5. The induction of some genes, such as the meristem identity genes, LEAFY and APETALA1 (AP1), and the flowering promotion gene CONSTANS (CO) can result in an early flowering phenotype. Mutant plants with defective copies of either of these genes are late flowering. When either of these genes is expressed in transgenic plants an early flowering phenotype is produced. An Arabidopsis LEAFY gene was used to introduce an early flowering phenotype to citrus that normally takes between six to twenty years to flower 6. However, this approach has not been successful with other species such as apples where no change in flowering time was observed in transgenic plants probably due to redundancy in the function of LEAFY.

EXECUTIVE SUMMARY

Project Title:
Genetic engineering of mangosteen (Garcinia mangostana L.) for early flowering

 

The MADS-box gene AGL20, now known as SOC1, appears to be important in control of flowering and does not appear to be redundant. In Arabidopsis SOC1 plays a role in inducing the expression of LEAFY. This indicates that this gene might be a central component for the induction of flowering 7. SOC1 gene is likely to be a better candidate gene to use to introduce the early flowering trait into mangosteen.
Tissue cultures of mangosteen from different explants had been reported 8, 9, 10, 11.The establishment of these mangosteen tissue culture methods will help to develop its transformation system. Several MADS-domain encoding genes were cloned from oil palm flowers 12. Recently AGL20 has been demonstrated to encode the same protein as that encoded by SOC113. The oil palm homologue of this gene was able to introduce an early flowering phenotype to transgenic Arabidopsis 14. This is the first example of a palm floral gene, controlling flowering in a dicot plant.

Research approach:

Initially the SOC1 (MADS-box) gene will be cloned by RT-PCR from mangosteen flowers at the correct developmental stage (determined by histology).A full-length gene will be isolated by screening a cDNA library constructed from mangosteen floral meristems. Gene expression during floral development will be determined by Northern blotting. An Agrobacterium transformation vector containing the SOC1 gene driven by a constitutive promoter (35S and or Ubiquitin) will be constructed.

When the construct is ready, the SOC1 gene will be transferred into mangosteen. In order to do so, technology for tissue culture, transformation and regeneration of mangosteen has to be in place. The Agrobacterium mediated transformation will be tested using reporter gene.

Output expected from the project:

1. New knowledge on mangosteen flowering development at the structural and molecular level.
2. Development of technology to promote early flowering.
3. Transformation and regeneration systems developed for mangosteen.
4. Greater team of expertise in the area of mangosteen genetic engineering.

Period of the project : 3 Years (2001 - 2004)

Achievements

Progress/Achievements for year one

Status

- On-going