Molecular cloning and characterization in eukaryotic expression systems of a sugarcane cysteine protease inhibitor gene involved in drought tolerance

Cystatin responses in sugarcane plants under drought stress have not previously been reported. To test the hypothesis that sugar cane cystatin can function as an osmotic stress tolerance gene, transgenic Pichia pastoris (GS115) and Saccharomyces cerevisiae (A2279) strains with the ability to express sugarcane cystatin were constructed. The osmotic stress tolerance of the transgenic yeasts was then evaluated, and it was found that the transgenic Pichia pastoris (GS115) and Saccharomyces cerevisiae (A2279) had increased growth and increased osmotic stress tolerance. To gain a greater understanding of the responses of sugarcane cystatin to drought, 1 drought-susceptible and 3 drought-tolerant sugarcane cultivars were grown in a greenhouse for 3 weeks, exposed to drought stress for 5 days, and rehydrated for 5 days. Semiquantitative RT-PCR was subsequently performed, and the results showed increased sugarcane cystatin gene transcription in stressed plants when compared to the control. There was a greater increase in the drought-tolerant versus the drought-susceptible cultivars. However, the mRNA levels decreased once the plants recovered from the drought conditions. Hence, this study shows that the expression of cystatin in sugarcane is involved in drought stress. This gene may also serve as a target for future breeding programs focused on stress tolerance in sugarcane.