SLAC1 gene discovery: Drought resistant crops may follow

Akhila Sachidanandam

There was a time when the earth’s atmosphere was devoid of oxygen. However, it became an integral component of the atmosphere though much later, as a result of byproduct of various organisms’ metabolisms. Since then a plethora of physiological changes lead to oxygen turning into the elixir of life. The percentage of oxygen and carbon dioxide in the atmosphere accounts to 21% and 0.03% respectively. Now that for most living organisms the ‘good gas’ is oxygen and the ‘bad gas‘ is carbon dioxide, how come oxygen hasn’t gotten depleted? What maintains the carbon dioxide oxygen ratio? Green plants and anaerobic bacteria utilize carbon dioxide for their food making process – photosynthesis during which oxygen is given out as a byproduct.

However, with increased burning of fossil fuels, green house gases ratio in the atmosphere has been raising steadily. To worsen it all, ozone level in the atmosphere is also in the forefront among the swelling undesirable gases. With increase in carbon dioxide level in the atmosphere, it is but natural to expect an elevation in photosynthetic activity and carbon sequestration in plants. But then, notably this was not the case – owing to increase in ozone level also in addition to carbon dioxide in the atmosphere.

Biologists from the University of California, University of Helsinki and two other European universities have observed that, ozone level content beyond the threshold causes the stomata of plants to close. Stomata are minute pores on the under and upper side of leaves formed by two bean shaped guard cells which controls the opening and closure of the pores. Ozone, on entering plants’ system results in the following changes:

1. Stomatal pores close

2. Damages chloroplast (chlorophyll containing organelles)

3. Minimizes photosynthetic activity

4. Interferes with respiratory mechanism resulting in low yield and stunted growth

Therefore, though closure of stomatal pores is a protective function in terms of carbon sequestration and ozone accumulation, it can also have deleterious effects as stated above. Meanwhile, Jaakko Kangasjarvi and his collaborators at the University of Helsinki in Finland discovered the gene that stimulates the opening and closure of stomata in response to increased ozone. They found an Arabidopsis plant whose pores did not close in response to ozone. The Slow Anion Channel 1 gene (SLAC1 gene) responsible for encoding a membrane protein was found to be mutated in this plant and was therefore non-functional. This membrane protein is apparently essential for the anionic channel in the guard cells to function, which invariably controls the opening and closure of stomata. While a normal SLAC1 gene closes stomata in response to elevated ozone level, abscisic acid and partially in response to elevated carbon dioxide, mutant SLAC1 gene, does not close the stomatal pores under these conditions.

This finding has given scientists the inkling to develop drought resistant crops, which will be a lucrative initiative for agriculture. Given that during draught, 95% of water loss takes place through the stomatal openings, scientists opine that further understanding of genetic and physiological modus operandi would be a stepping-stone to produce drought resistant crops by genetic engineering.