Identification Of Transgenic Rice With Rnai-silenced OsABA8ox2and Expression Analysis Of ABA Related Genes

Abscisic acid (ABA) is a plant hormone which plays an important role in a seriesof physiological processes, such as plant growth and development. Endogenous activeABA is not only a cell signal but also a stress-responsive signal. The levels ofendogenous ABA content are modulated mainly by its synthetic and catabolic rate. Thehydroxylation of ABA catalyzed by ABA8’-hydroxylase is known as the key step ofABA catabolism. OsABA8ox1, OsABA8ox2and OsABA8ox3are three ABA8’-Hydroxylase genes in rice. However, the function and underlying mechanisms ofOsABA8ox2in rice remain to be investigated. In this study, Realtime q-PCR and othermethods were used to study T2generation of OsABA8ox2-RNAi transgenic rice indepth. Positive plants of transgenic rice were identifed. The expression of OsABA8oxgene family and ABA related genes were assayed. The agronomic characters ofOsABA8ox2-RNAi transgenic rice were statistically analysised. This study wouldprovide a theoretical basis for defining function of OsABA8ox2in ABA catabolicpathways，and also supply the reference to the study of rice response to resistance andunderstanding the mechanisms of endogenous hormones.The main results obtained are as follows:1、Realtime q-PCR results showed that OsABA8ox are expressed in roots, stemsand leaves in rice Kitaake. Expression of OsABA8ox1and OsABA8ox2in leaves is thehighest, followed by the roots and stems. The highest expression of OsABA8ox3is inroots and the minimum amount expression is in leaves.2、12transgenic rice lines of down-regulation OsABA8ox2were identified byPCR and GUS-staining. The realtime q-PCR assay showed that down-regulatedtranscript levels of OsABA8ox1and OsABA8ox2in OsABA8ox2-RNAi transgenic plantswhich leaded to the increase of the expression of ABA synthetic genes, OsZEP andOsNCED1, and endogenous ABA content.3、In3-leaf-stage seedlings of OsABA8ox2-RNAi transgenic rice the survival ratewere evidently elevated under drought or salt treatment. After10days under droughttreatment, the survival rate is60％and32％in RNAi and WT lines respectively. After 10days under salt treatment, the survival rate is54％and22％in RNAi and WT linesrespectively. Several genes beneficial to rice tolerance to stress were up-regulated inOsABA8ox2-RNAi plants, such as OsMyb4， OsCAT， OsCLC-1， OsHKT6，OsbZIP71and OsbZIP23.5、Down-regulation of OsABA8ox1and OsABA8ox2produced great phenotypicimpacts, including delayed seed germination, dwarfism, decreased tiller number andreduced seed set. OsABA8ox2-RNAi transgenic rice showed a2-day-long delay and alower germination rate in seed germination. Height of OsABA8ox2-RNAi transgenicrice decreased to approximately60％of WT. Setting percentage of OsABA8ox2-RNAitransgenic rice showed approximately42~56％of WT.