The Role Of Microtubule Cytoskeleton On Mesocotyl Elongation In Northern Weedy Rice

Mesocotyl length is one of the important factors affecting the rice seedling. There is some subspecie differences in mesocotyl elongation in cultivated rice. Most of the mesocotyl elongation ability in Indica rice is strong, but mesocotyl elongation in japonica rice is weak. Earlier research found that japonica genetic background of weedy rice (Oryza sativa f. spontanea L.)——WR04-6 and WR04-43 have longer mesocotyls, but its mechanisms of mesocotyl elongation are largely unknown.Rice mesocotyl elongation is determined by cell growth, division and morphogenesis. Microtubule cytoskeleton (MT) are major components of the cytoskeleton and they involve in the regulation of cell growth, division and morphogenesis. However, role of mesocotyl on microtubules in rice is not clear. This research uses weedy rice WR04-6 and WR04-43 as test materials, cultivated rice Nipponbare as control to clarify mechanism of mesocotyl elongation of weedy rice though microtubule depolymerization mediated GA content. Major findings are as follows:1. MT-destabilizing agent oryzalin treatment (25 nM) leads to the remarkable increase of rice mesocotyl, which is correlated with mesocotyl cell elongation. In contrast, mesocotyl length and cell length was reduced with the treatment of MT-stabilizing reagent taxol (1μM).2. Compared to Nipponbare, weedy rice displayed more extensive disassembly in the early stage of mesocotyl elongation and subsequent more transversely oriented MTs.3. Early disassembly in weedy rice stimulates the production of endogenous GAs and induced the high expression of GA20ox2, GA3ox2, and GTD1.4. By analyzing the expression of 15 MAP (microtubule-associated protein) genes, three OsKatanin (a serving-MT protein) subunit genes showed significant expression in early weedy rice mesocotyl elongation.5. Two OsKatanin p60s subunit genes were respectively over-expressed in cultivated rice Nipponbare, resulting in the obvious increase of mesocotyl and mesocotyl cell length. Changes of MT organization, G A content and G A biosynthesis gene expression in over-expression plants were similar with these in weedy rice.In a word, MT dynamics on mesocotyl elongation of Northern weedy rice play an important regulating role. MT disassembly mediated by Oskatanin has an obvious effect on the increase of GA content therefore produces significantly longer weedy rice mesocotyls.