Expansin Involved In Drought-Resistance Of Land Rice

Expansin is cell-wall protein that catalyzes long-term expansion of cell walls.lt has been proposed that expansins have rather diverse effects throughout the whole developmental process,for example, control of organ size, morphology, fruit maturation and abscission and so on. However, the role mechanism of expansins during plant growth,especially the role mechanism on root development under the drought stress is still poorly understood despite of much research effort. In this study,we reserch its localization in the root ,expression characters and possible role mechanism on the root development of land rice under drought stress.In this research,according to two a -expansin genes OsEXPS and OsEXP5 of rice reported in gene bank ,we design a pair of primers and clone the two expansin genes from the roots of four land-rice varietes with the method of RT-PCR .The results prove that the two genes have expression in land rice root.Also we study their expression characters through the method of northern-blot.The results show they have different expression in different developmental stages :the OsEXP3 gene has high expression in 3-d-old root and 20-d-old root,but low expression in 8-d-old root,furthermore there are the same result in three land rice such as IRAT109,haogelao,and land ricel.For the OsEXP5 gene of land rice IRAT109,there is high expression in 3-d-old root,but little expression in 8-d-old root; And the expression of OsEXP3 and OsEXP5 gene enhance in 8-d-old root treated with 50mol/l ABA for three hours;The drought signal can also promote their expression but their expression reduce to control level after rewatering.The OsEXPS gene has different expression in different drought-resistant land rice: higher expression in the high drought-resistant land rice than the low drought-resistant land rice. We also found the two genes have different expression pattern under drought stress:the expression of the OsEXPS gene in 3-d-old root enhance but OsEXP5 in 3-d-old root has no change under drought stress.however the OsEXP5 gene in 8-d-old root increase its expressin under drought stress.According to these results we infer the two genes may make effects in different development stage on drought-resistance of land rice .And their expression is regulated positivly by hormone.Furthermore.we study the localization of expansin in the land-rice root through immunohistochemical method so as to find the possible role mechanism of expansin .The result shows that expansins are preferentially present in the epidermal cells and outside cortex in the region of elongation in the primary root,also present in inside cortex, pericycle and vascular tissues, but not in thin-walled cortex cell .However in the region of maturation,the expansis have low expression level only in the epidermal cells and outside cortex and have no expression in inside cortex, pericycle,vascular tissues and thin-walled cortex cell. In contrast to the primary root , in the lateral root and adventitious root, the expansin proteins are present in all type of cell walls. These results indicate that expansin not only express in root but also involve in the development of the root,especially accelerating the development of the lateral root and adventitious root.We has carried out an investigation to understand root development by anti-expansin and the tranformed AtEXPl tobacco. The result indicates that they play important roles on the development of lateral and adventitious roots.According to above results, we infer that the expansins are involved in the drought-resistance of land rice through accelerating the development of the lateral root and adventitious root possibly.