Abstract
BackgroundAs the final stage of leaf development, leaf senescence may cause the decline of photosynthesis and gradual reduction of carbon assimilation, which makes it a possible limiting factor for crop yield. NACs are plant-specific transcription factors and some NACs have been confirmed to play important roles in regulating leaf senescence.ResultsIn this study, we reported a member of the NAC transcription factor family named OsNAP whose expression is associated with leaf senescence, and investigated its preliminary function during the process of leaf senescence. The results of qRT-PCR showed that the OsNAP transcripts were accumulated gradually in response to leaf senescence and treatment with methyl jasmonic acid (MeJA). A subcellular localization assay indicated that OsNAP is a nuclear-localized protein. Yeast one-hybrid experiments indicated that OsNAP can bind the NAC recognition site (NACRS)-like sequence. OsNAP-overexpressing transgenic plants displayed an accelerated leaf senescence phenotype at the grain-filling stage, which might be caused by the elevated JA levels and the increased expression of the JA biosynthesis-related genes LOX2 and AOC1, and showed enhanced tolerance ability to MeJA treatment at the seedling stage. Nevertheless, the leaf senescence process was delayed in OsNAP RNAi transgenic plants with a dramatic drop in JA levels and with decreased expression levels of the JA biosynthesis-related genes AOS2, AOC1 and OPR7.ConclusionsThese results suggest that OsNAP acts as a positive regulator of leaf senescence and this regulation may occur via the JA pathway.
Highlights
As the final stage of leaf development, leaf senescence may cause the decline of photosynthesis and gradual reduction of carbon assimilation, which makes it a possible limiting factor for crop yield
Other 9 genes are expressed in leaves, but only the transcripts of OsNAP, OsNAC5 and OsNAC6/SNAC2 in leaves are up-regulated during leaf senescence [25,26,27]
Several studies have demonstrated that OsNAC5 and OsNAC6/SNAC2 are involved in stress tolerance in rice [28,29,30]
Summary
As the final stage of leaf development, leaf senescence may cause the decline of photosynthesis and gradual reduction of carbon assimilation, which makes it a possible limiting factor for crop yield. NACs are plantspecific transcription factors and some NACs have been confirmed to play important roles in regulating leaf senescence. As the final stage of leaf development, leaf senescence eventually leads to leaf death, which is controlled by both internal and external factors. It has been reported that many NACs show enhanced expression during dark-induced and natural leaf senescence in Arabidopsis [4,5], and may play a central role in mediating leaf senescence. The senescence-controlling NAC gene NAM-B1 was reported to be associated with the contents of grain protein, zinc, and iron in wheat [6]. ANAC092/AtNAC2/ORE1, whose expression correlates with senescence, positively regulates aging-induced cell death in Arabidopsis leaves [7]. The oresara (ore1) mutant, which lacks the functional ANAC092/AtNAC2/ORE1 gene, displays a delayed leaf senescence phenotype [8]
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