Functional analysis of Oryza sativa NAC054 transcription factor during leaf senescence

Abstract

Leaf senescence, the final stage of leaf development, is regulated by complex network of senescence associated genes (SAGs). Several NAC transcription factors have been found to regulates leaf senescence in Arabidopsis, but only a few senescence associated NAC TFs have been identified in rice. In this study, we identified new senescence-associated NAC TF in rice, OsNAC054. We found OsNAC054 expression increased during senescence. osnac054-1 T-DNA KO mutants stayed green during dark-induced and natural senescence condition, suggesting OsNAC054 acts as senescence promoting NAC TF. By microarray and qRT-PCR analysis, several SAGs (OsORE1.1, OsNAP, OsEIL1) and Chl degradation associated genes (OsSGR, OsNYC1, OsPAO) were down-regulated in osnac054-1 under DIS condition. Furthermore, we found that OsNAC054 expression is induced by ABA, and osnac054-1 mutants showed stay-green phenotype during ABA induced senescence, strongly indicating that OsNAC054 regulates leaf senescence through ABA-signaling pathway. Also, OsNAC054 is Membrane bound TFs (MTFs) that have a transmembrane (TM) domain at its C-terminus. By transient expression assay using epidermal onion cell, we identified TM region of OsNAC054. We found that TM deleted OsNAC054 localized only in the nucleus, while full length OsNAC054 localized both inside and outside of nucleus. Thus, it is possible that TF activity of OsNAC054 is controlled by proteolytic cleavage of TM. Our data suggest that OsNAC054 is involved in the promotion of leaf senescence through ABA-signaling pathway.