Bacterial diversity in the rhizosphere of AVP1 transgenic cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.)

Genetic modification of plants to incorporate useful traits is a powerful technology for the future development of sustainable agricultural systems. The first commercially grown genetically modified food crop was tomato (called Flavr Savr), which was modified to slow its ripening (Belinda, 2001). In 1996, the first genetically modified seeds were planted in the United States for its commercial use. Ten years later, genetically modified crops were grown on 102 million hectares worldwide. In 2008, the cultivation of GM crops grew worldwide by covering 125 million hectares (James, 2008).Cotton and wheat are two major crops of Pakistan grown on large area of the country. During 2008-09 area under wheat cultivation was 9062 thousand hectares and production was 23.4 million tons, 11.7% more than the last year. Cotton was sown on the area of 2820 thousand hectares, 7.7% less than the last year (3054 thousand hectares) and production was 11.8 million bales, which was higher by 1.1% over the last year (11.7 million bales) (Economic survey of Pakistan 2009).There is a great tendency among the farmers for the cultivation of genetically modified crops. Transgenic crops engineered to tolerate some measure of drought could significantly increase yields for many developing countries and help to alleviate an increasingly imminent threat of famine. Overexpression of the H+pyrophosphatase (H+PPase) AVP1 results in salt and water stress tolerance in Arabidopsis plants (Gaxiola et al., 2001). The tolerance was initially explained by an enhanced uptake of ions into their vacuoles. Presumably, the greater AVP1 activity in vacuolar membranes provides increased vacuolar H+ to drive the secondary active uptake of toxic (i.e. sodium) and nontoxic ions into the vacuole. The resulting decline in vacuolar osmotic potential may trigger water uptake, permitting plants to survive under conditions of low soil water potentials (Gaxiola et al., 2002). Significantly, further characterization of these AVP1 overexpressing plants revealed a dramatic enhancement of their root development, with obvious implications for their ability to withstand drought (Li et al., 2005). These results suggest that the H+PPase AVP1 is a potential target for genetic engineering of root systems in agriculturally important crop plants.Soil microbes play important roles in various aspects of the terrestrial ecosystem, such as soil fertility during plant growth and biogeochemistry of the cycling of organic and non-organic compounds through entire natural ecosystem. Soil biota mediate or regulate a variety of functions essential for plant growth and productivity, soil resource structure, and ecosystem health. Plant growth promoting rhizobacteria present in the rhizosphere are one of the best characterized functional group microorganisms known for playing a significant role in plant health and plant development (Siddiqui, 2006) and responsible for numerous functions including nutrient cycling and decomposition, which can significantly influence vegetation dynamics (Kent & Triplett, 2002). It can be assumed that any significant impact of plant over expression of AVP1 gene through genetic transformation might alter the basic fundamental microbial processes, like biological nitrogen fixation.