Populus euphratica miR1444b positively regulates plants response to drought stress in Arabidopsis thaliana

Objective miR1444b is a member of woody plant specific miR1444 family participating in plant response to metal stress. However, its function in response to drought stress is unknown.

Method We isolated Populus euphratica MIR1444b gene (peu-MIR1444b) and its promoter (pro-peu-MIR1444b), then overexpressed peu-MIR1444b gene at the model plant Arabidopsis thaliana. The peu-MIR1444b gene's function was analyzed under normal watering, mannitol-simulated drought and natural soil drought conditions.

Result We compared the genomic sequence homology of Populus trichocarpa collected from the Phytozome database with the pro-peu-MIR1444b and peu-MIR1444b, which sharing 99.61% and 98.82% similarity, respectively. Analysis using the PlantCARE database revealed that the pro-peu-MIR1444b sequence contained the stress-related TC-rich repeat elements and the drought-induced MYB binding site MBS. QRT-PCR results showed that transgenic lines had significantly higher expression level of miR1444b than in wild type, the expression level of target gene glucan synthase-like Ⅳ (AT3G14570.2) was down-regulated, and it indicated that glucan synthase-like Ⅳ was negatively regulated by peu-miR1444b in A. thaliana. Under 250 mmol/L mannitol-simulated drought stress condition, germination rate of TG-2 and TG-5 in transgenic lines was significantly higher than wild-type by 20.83% and 26.67%, and their root length was drastically higher than wild-type by 56.83% and 52.60%(P < 0.05), respectively. At 8 days after natural soil drought treatment, photosynthetic rate, stomatal conductance, PSⅡ maximum photochemical efficiency, leaf water use efficiency and peroxidase (POD) activity in transgenic lines were obviously higher than those in wild type (P < 0.05).

Conclusion Our study reveals that miR1444b increases water absorption capacity of plants by promoting root growth, negative regulation of glucan synthase-like Ⅳ enhance plant osmotic adjustment ability to maintain plant photosynthetic efficiency under water deficit environment, ensure the normal growth of plants. miR1444b positively regulates plant response to drought stress in A. thaliana.