Cloning And Functional Analysis Of ZmSNACl In Maize (Zea Mays L.) And SbSNACl Gene In Sorghum [Sorghum Bicolor (L.)Moench]

Abiotic stresses that cause adverse effects on the growth and development of plants. Thephysiologic response to these stresses arises out of changes in gene expression. The products of thesestress induced genes can be classified into two groups: functional genes and the regulatory genes thatinvolved in signal transduction in the stress response. NAC proteins are plant-specific transcriptionfactors that play essential roles in stress responses. However, only little information regardingstress-related NAC genes is available in grass family such as maize and sorghum. In this study, wecharacterized two NAC family members which were designed as ZmSNAC1and SbSNAC1. Weexamined their expression profiles and analyzed their abiotic stress-related functions, respectively.1. Isolation and functional analysis of maize ZmSNAC1A maize NAC gene, ZmSNAC1, was isolated from the maize inbred line “CN165” and functionallycharacterized. ZmSNAC1had more close relationship with rice SNAC1according to the phylogeneticanalysis. Expression analysis revealed that ZmSNAC1was strongly induced by low temperature, highsalinity, drought stress, and abscisic acid (ABA) treatment, but downregulated by salicylic acid (SA)treatment. Subcellular localization experiments in Arabidopsis protoplast cells indicated that ZmSNAC1was localized in the nucleus. Transactivation assays demonstrated that ZmSNAC1functioned as atranscriptional activator. Overexpression of ZmSNAC1in Arabidopsis led to hypersensitivity to ABAand osmotic stress at the germination stage, but enhanced tolerance to dehydration compared towild-type (WT) seedlings. Moreover, over-expression of ZmSNAC1in Arabidopsis conferred enhanceddrought and salt tolerance, which was supported not only by the improved survival percentage inZmSNAC1transgenic lines compared with the WT lines but also by physiological changes, such as thereduced electrolyte leakage and higher chlorophyll content in transgenic plants. These results indicatedthat ZmSNAC1may function as a positive regulator in multiple pathways of plants response to abioticstresses and is potentially useful in transgenic breeding to improve stress tolerance in crops.2. Isolation and functional analysis of sorghum SbSNAC1SbSNAC1is a member of the plant-specific NAC transcription factor superfamily that plays animportant role in the abiotic stress response in sorghum. The SbSNAC1protein consists of a typicalNAC conserved domain at its N terminus and a diverse C-terminal region. The expression of SbSNAC1was induced by various abiotic stresses, such as drought and salinity. SbSNAC1is also expressed at arelatively higher concentration in roots and responds to the phytohormone abscisic acid. Transactivationanalysis indicated that the transactivation activity of SbSNAC1is located in the C-terminal region,whereas no activity was detected in the conserved NAC-domain, localized in the N-terminus. The testedregion (215-235aa) of the C-terminus was considered to be necessary for its transactivation activity.Subcellular localization assays using constructs of different SbSNAC1fragments fused with greenfluorescent protein revealed that the SbSNAC1protein localized in the nucleus, and that the nuclearlocalization signal was present in the N-terminal section. Furthermore, transgenic plants overexpressingSbSNAC1had an improved drought stress tolerance compared with wild-type plants, but no obviousretardation was detected in plant growth and development. SbSNAC1-overexpressed transgenic plants showed increased transcription of the stress-responsive genes under drought treatment. These resultssuggest that SbSNAC1functions as a stress-responsive transcription factor in positive modulation ofabiotic stress tolerance, and may have applications in the engineering of drought-tolerant crops.