Regulation of rose petal dehydration tolerance and senescence by RhNAP transcription factor via the modulation of cytokinin catabolism

Abstract

Petals and leaves share common evolutionary origins but have different phenotypic characteristics, such as the absence of stomata in the petals of most angiosperm species. Plant NAC transcription factor, NAP, is involved in ABA responses and regulates senescence-associated genes, and especially those that affect stomatal movement. However, the regulatory mechanisms and significance of NAP action in senescing astomatous petals is unclear. A major limiting factor is failure of flower opening and accelerated senescence. Our goal is to understand the finely regulatory mechanism of dehydration tolerance and aging in rose flowers. We functionally characterized RhNAP, an AtNAP-like transcription factor gene that is induced by dehydration and aging in astomatous rose petals. Cytokinins (CKs) are known to delay petal senescence and we found that a cytokinin oxidase/dehydrogenase gene 6 (RhCKX6) shares similar expression patterns with RhNAP. Silencing of RhNAP or RhCKX6 expression in rose petals by virus induced gene silencing markedly reduced petal dehydration tolerance and delayed petal senescence. Endogenous CK levels in RhNAP- or RhCKX6-silenced petals were significantly higher than those of the control. Moreover, RhCKX6 expression was reduced in RhNAP-silenced petals. This suggests that the expression of RhCKX6 is regulated by RhNAP. Yeast one-hybrid experiments and electrophoresis mobility shift assays showed that RhNAP binds to the RhCKX6 promoter in heterologous in vivo system and in vitro, respectively. Furthermore, the expression of putative signal transduction and downstream genes of ABA-signaling pathways were also reduced due to the repression of PP2C homolog genes by RhNAP in rose petals. Taken together, our study indicates that the RhNAP/RhCKX6 interaction represents a regulatory step enhancing dehydration tolerance in young rose petals and accelerating senescence in mature petals in a stomata-independent manner.

The leaf senescence-promoting transcription factor AtNAP activates its direct target gene CYTOKININ OXIDASE 3 to facilitate senescence processes by degrading cytokinins

“…We now reveal that AtNAP TF can also facilitate the senescence processes by activating its direct target AtCKX3 to degrade CKs. Similar to the AtNAP-AtCKX3 module, the RhNAP-RhCKX3 module in rose has been reported to regulate petal senescence by degrading CKs; RhNAP in rose is an orthologue of AtNAP (Zou et al, 2021). We also found that Both OsNAP in rice and AtNAP could bind to the promoter of OsCKX8 (but not OsCKX9) in rice as revealed by the yeast one-hybrid analyses (Supplemental Fig.…”

“…It is well known that CKs inhibit leaf senescence (Gan and Amasino, 1995;Gan and Amasino, 1996;Gan and Amasino, 1997;Gan, 2010;Guo et al, 2021), and that the CK concentrations decrease rapidly at the onset of and during senescence in leaves and flowers (Gan and Amasino, 1996;Zou et al, 2021). Our research revealed a novel ABA-CK crosstalk mechanism by which the ABA-induced TF AtNAP physically binds to the promoter of AtCKX3 to activate the expression of the enzyme that subsequently catabolizes CKs and facilitates the senescence processes (Fig.…”

LcNAC13 Is Involved in the Reactive Oxygen Species-Dependent Senescence of the Rudimentary Leaves in Litchi chinensis

“…The phylogenetic tree indicated that LcNAC13 in litchi had the highest similarity with NAP in Arabidopsis . Meanwhile, NAP is well known as a central factor in the regulation of plant senescence ( Luoni et al, 2019 ; Zou et al, 2021 ). Hence, it is likely that LcNAC13 may be an important factor regulating senescence in litchi leaves.…”

A positive feedback regulatory loop, SA-AtNAP-SAG202/SARD1-ICS1-SA, in SA biosynthesis involved in leaf senescence but not defense response

“…The role of NAP orthologues in leaf senescence has been demonstrated in wheat (Uauy et al, 2006), maize (Zhang et al, 2012b), rice (Liang et al, 2014), cotton (Fan et al, 2015), peach (Li et al, 2016), and cabbage (Li et al, 2021). NAP also has a major role in senescence of rose petals (Zou et al, 2021) and Arabidopsis fruits (Kou et al, 2012). The direct target genes of AtNAP are of significant interest for understanding the molecular circuitry of leaf senescence regulation.…”

“…It is known that AtNAP TF directly binds to the promoter of SAG113 to activate the expression of a senescencespecific and Golgi-localized protein phosphatase 2C gene to promote senescence (Zhang and Gan, 2012;Zhang et al, 2012a). The TF also physically binds to the promoter of cytokinin oxidase genes in Arabidopsis, rice (Hu et al, 2021) and rose (Zou et al, 2021) to degrade the senescence-retardant cytokinins, which facilitates the senescence process.…”