Identification of up-regulated genes in flag leaves during rice grain filling and characterization of OsNAC5, a new ABA-dependent transcription factor

Abstract

Rice is a poor source of micronutrients such as iron and zinc. To help clarify the molecular mechanisms that regulate metal mobilization from leaves to developing seeds, we conducted suppression subtractive hybridization analysis in flag leaves of two rice cultivars. Flag leaves are the major source of remobilized metals for developing seeds. We isolated 78 sequences up-regulated in flag leaves at the grain filling stage relative to the panicle exertion stage. Differential expression of selected genes (encoding 7 transport proteins, the OsNAS3 enzyme and the OsNAC5 transcription factor) was confirmed by quantitative RT-PCR. We show that OsNAC5 expression is up-regulated by natural (aging) and induced senescence processes (dark, ABA application, high salinity, cold and Fe-deficiency) and its expression is not affected in the presence of 6-benzylaminopurine (a senescence inhibitor) under dark-induced senescence. Salt induction of OsNAC5 expression is abolished by nicotinamide, an inhibitor of ABA effects. This result and the presence of cis-acting elements in the promoter region of the OsNAC5 gene suggest an ABA-dependent regulation. Using four different rice cultivars, we show that OsNAC5 up-regulation is higher and earlier in flag leaves and panicles of IR75862 plants, which have higher seed concentrations of Fe, Zn and protein. We suggest that OsNAC5 is a novel senescence-associated ABA-dependent NAC transcription factor and its function could be related to Fe, Zn and amino acids remobilization from green tissues to seeds.

PvNAC1 and PvNAC2 Are Associated with Leaf Senescence and Nitrogen Use Efficiency in Switchgrass

“…Repression of four homologs of NAM-B1 in a hexaploid wheat, via RNA interference (RNAi), delayed plant senescence by more than 3 weeks and reduced grain protein, zinc, and iron content by more than 30 %, while flag leaves of RNAi plants retained more residual nitrogen, zinc, and iron than wild-type controls [11]. Rice OsNAC5 was found to be induced earlier and to a greater extent in flag leaves and panicles of rice cultivars with higher seed protein content, indicating that OsNAC5 may be involved in amino acid remobilization from green tissues to seeds [12]. Although there have been some microarray-based transcriptomic studies of senescence in Arabidopsis [13][14][15], Populus [16], wheat [17], and barley [18], little is known about processes that are regulated directly by NAC TFs.…”

“…Phylogenetic analysis of various plant NAC TFs grouped PvNAC1 and PvNAC2 with AtNAP, TtNAM-B1, and OsNAC5, each of which have been implicated in senescence and/or nutrient remobilization [22,11,12] (Fig. 1).…”

“…1 Phylogenetic analysis of PvNAC1 and PvNAC2 with representative rice NACs as well as other NACs with known or indicative functions. The branch within the dashed box includes PvNAC1 and PvNAC2 (indicated by solid arrows) and NAC TFs related to senescence in Arabidopsis (AtNAP) [22] and nutrient remobilization in wheat (TtNAM-B1) [11] and rice (ONAC009/OsNAC5) [12] (indicated by empty arrows). Confidence levels are shown as percentages with a possible role of PvNAC1 and PvNAC2 in the regulation of leaf senescence.…”

Overexpression of a NAC transcription factor delays leaf senescence and increases grain nitrogen concentration in wheat

“…2012), rice ( Oryza sativa ; Sperotto et al . 2009), bamboo ( Bambusa emeiensis ; Chen et al . 2011) and barley (Christiansen & Gregersen 2014).…”

A structural view of the conserved domain of rice stress-responsive NAC1

“…OsNAC6, an ATAF homolog in rice, is rapidly and strongly induced by cold, salt, drought, abscisic acid, jasmonic acid and wounding, indicating its role in both biotic and abiotic responses (Ohnishi et al, 2005;Nakashima et al, 2007). Recently, OsNAC5, like OsNAC6, was characterized as a transcriptional activator that enhances stress tolerance by upregulating the expression of stress-inducible rice genes (Sperotto et al, 2009;Takasaki et al, 2010). Using mRNA differential display, StNAC, an ATAF homolog in potato, was found to be induced early after wounding (Collinge and Boller, 2001).…”