The investigation of gene expression of Myosin genes under drought stress in potato different tissues

Potato (Solanum tuberosum L.) is an economic crop that is grown and consumed worldwide. Potato is considered as the fourth important crop for human consumption after maize, wheat, and rice. Potato contain more carbohydrates, proteins, minerals, and vitamins per unit area than cereals. However, this crops exposed environmental stresses during growth and developmental stages particularly, drought stress. Potato is sensitive to drought condition because of narrow root system. As a result, it is necessary the investigation of molecular mechanism involved in drought stress in potato. Drought stress affected on the integrity and structure maintain of biological membrane. The actin-based myosin is necessary for the growth and organization of the endomembrane system. Given that myosin genes allow to move intercellular and intracellular providing the possibility of repair of damaged membrane areas under drought stress in plants. In eukaryotic cells, organelle movement, positioning and communications are critical for maintaining cellular functions and are highly regulated by intracellular trafficking. Directional movement of motor proteins along the cytoskeleton is one of the key regulators of such trafficking. Most plants have developed a unique actin–myosin system for intracellular trafficking. Myosins participate in a different cellular processes, endocytosis, containing cell polarization, intracellular and organellar transport, transcriptional regulation, and signal transduction. Motions are as molecular motors in biological systems. These can bind to filamentous actin and produce physical forces through hydrolyzing ATP. Myosins is one of the most diverse and largest protein families in eukaryote. Class XI and VIII motor proteins are characterized as a slow and fast motor proteins. Myosin XI possess many genes in Angiosperms. Whereas, myosin-VIII contain fewer members against class XI. Further, molecular size of myosin-VIII is smaller than myosin-XI.

Protein file of A.thaliana was downloaded and matrix file of hidden Markov Model (HMM) of myosin gene family was used. Here, phylogenetic analysis, gene structure, and gene expression were surveyed. Gene expression of two genes (StMyoXI-F and StMyoXI-B) was performed in different tissues (root, stem, leaves, and tuber). For analysis of expression in different tissues (leaves, stem, and root), sampling was performed 2 weeks after mother tuber growth. However, tubers were sampled 6 weeks after cultivated in Karaj. To evaluate expression under drought stress, after 6 weeks of growth, the water stress was induced by irrigation suppression in 2 weeks while, daily irrigation was maintained for control plants. Leaves and tuber sampling were performed under two conditions.

The seven StMyo genes were unevenly distributed in the two subgroups. The seven StMyo genes were unevenly distributed in the two subgroups. Class XI was the largest subfamily, which class VIII had the lowest subfamily. Drought treatment significantly increased expression of StMyoXI-B and StMyoXI-F genes by 80 and 8 fold compared to the control treatment, repectively. Under control conditions, StMyoXI-B and StMyoXI-F enhanced expression in root by 25 and 20 fold while, it showed low expression in leaves under control conditions. Under control conditions, StMyoXI-F gene showed the 3 and 4 fold change higher mean relative expression than the reference gene. The relative expression of StMyoXI-B gene has been increased 5 and 10 fold change in leaves and stem under non-stress conditions as compared to the reference gene. Among myosin genes, the number of exons varied from 1 to 39. Most of class-VIII proteins had fewer introns whereas, class-XI proteins possess more proteins than class VIII. This results indicated that occurred splicing process in the myosin genes.

Based on the obtained results, it is considered that these genes highly do not influenced in stem development. However, it had significantly affected in root, leaves, and tuber development. It seems this gene can be potentially a good candidate for drought tolerance breeding programs in potato.