Drought, salinity and heat affect plant growth and decrease crop yield. There are genes that confer tolerance to these stresses. Overexpressing the tonoplast H+ pyrophosphatase gene makes Arabidopsis drought and salt tolerant. Similarly, overexpressing the Rubisco activase gene helps improve photosynthesis under heat stress conditions.
What if we combine the two, wondered Neelam Mishra, St Joseph’s College, Bengaluru. She collaborated with researchers in the US and China to explore the possibility.
But there was a minor problem. Rubisco-activase becomes inactive over 30 degrees centigrade. So, the team sourced the gene from a desert plant, Larrea tridentata, where the gene product was heat tolerant.
The researchers introduced both genes into Arabidopsis. The transgenic plants thus developed were bred to the third generation to stabilise the genes within the plants.
The team then selected three types of transgenic plants. The first and second had single genes, while the third had a combination of both. They tested the plants under individual drought, salt, and heat stress as well as under combined stresses.
Under drought stress, plants that overexpressed the pyrophosphate gene and plants that overexpressed both genes performed better than wild type plants.
As in the case of drought stress, overexpression of the Rubisco-activase gene did not have any significant impact, but plants having extra pyrophosphate genes and the combination of the two genes did well, increasing seed yield by 50 per cent.
When exposed to heat stress, the Rubisco-activating gene as well as the combination of both genes contributed to healthy plant growth and yield. Interestingly, plants with an extra pyrophosphatase gene also performed better than non-transgenic plants. This could be due to the gene’s role in transporting auxins, the growth hormone, say the scientists.
When the plants were exposed to drought and heat stresses together, seed yield was 580 per cent more in double overexpression plants.
‘The two genes seemed to have additive interactions, enhancing tolerance to multiple stresses. The finding can be used to increase agricultural productivity under multiple abiotic stress conditions’, says Neelam Mishra.
Plant Science: 296: 110499 (2020); DOI: 10.1016/j.plantsci.2020.110499
Aradhana L Hans
Babasaheb Bhimrao Ambedkar University, Lucknow