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Summary: An NAC-type transcription factor gene AtNAC2 was identified from Arabidopsis thaliana when expression patterns of the genes from a microarray analysis were examined. The AtNAC2 expression was induced by salt stress and this induction was reduced in magnitude in the transgenic Arabidopsis plants overexpressing tobacco ethylene receptor gene NTHK1. AtNAC2 is localized in the nucleus and has transcriptional activation activity. It can form a homodimer in yeast. AtNAC2 was highly expressed in roots and flowers, but less expressed in other organs examined. In addition to the salt induction, the AtNAC2 can also be induced by abscisic acid (ABA), ACC and NAA. The salt induction was enhanced in the ethylene overproducer mutant eto1-1, but suppressed in the ethylene-insensitive mutants etr1-1 and ein2-1, and in the auxin-insensitive mutant tir1-1 when compared with that in wild-type plants. However, the salt induction of AtNAC2 was not significantly affected in the ABA-insensitive mutants abi2-1, abi3-1 and abi4-1. These results indicate that the salt response of AtNAC2 requires ethylene signaling and auxin signaling pathways but does not require ABI2, ABI3 and ABI4, intermediates of the ABA signaling pathway. Overexpression of AtNAC2 in transgenic Arabidopsis plants resulted in promotion of lateral root development. AtNAC2 also promoted or inhibited downstream gene expressions. These results indicate that AtNAC2 may be a transcription factor incorporating the environmental and endogenous stimuli into the process of plant lateral root development.

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