The NAC Transcription Factor SlNAP2 Regulates Leaf Senescence and Fruit Yield in Tomato

Abstract

Leaf senescence is an essential physiological process in plants that supports the recycling of nitrogen and other nutrients to support the growth of developing organs, including young leaves, seeds, and fruits. Thus, the regulation of senescence is crucial for evolutionary success in wild populations and for increasing yield in crops. Here, we describe the influence of a NAC transcription factor, SlNAP2 ( NAC-like, activated by Apetala3/Pistillata), that controls both leaf senescence and fruit yield in tomato (). expression increases during age-dependent and dark-induced leaf senescence. We demonstrate that SlNAP2 activates (), a homolog of Arabidopsis () , chlorophyll degradation genes such as ( senescence-inducible chloroplast stay-green protein 1) and ( pheide oxygenase), and other downstream targets by directly binding to their promoters, thereby promoting leaf senescence. Furthermore, SlNAP2 directly controls the expression of genes important for abscisic acid (ABA) biosynthesis, 9-cis-epoxycarotenoid dioxygenase 1 (); transport, ABC transporter G family member 40 (); and degradation, ABA 8'-hydroxylase (), indicating that SlNAP2 has a complex role in establishing ABA homeostasis during leaf senescence. Inhibiting expression in transgenic tomato plants impedes leaf senescence but enhances fruit yield and sugar content likely due to prolonged leaf photosynthesis in aging tomato plants. Our data indicate that SlNAP2 has a central role in controlling leaf senescence and fruit yield in tomato.

MdbHLH93, an apple activator regulating leaf senescence, is regulated by ABA and MdBT2 in antagonistic ways

“…The plant hormone ABA triggers and promotes the senescence process (Cutler et al, 2010). The NAC TFs NAP and NAC2 are well known to be involved in ABA-promoted leaf senescence by regulating the transcription of chlorophyll degradation genes and ABA metabolic genes in Arabidopsis, rice and tomato (Zhang & Gan, 2012;Liang et al, 2014;Yang et al, 2014;Mao et al, 2017;Ma et al, 2018). However, beyond these, there are few reports of regulators in ABA-promoted leaf senescence, and the underlying molecular mechanism of ABA-modulated leaf senescence is unclear.…”

Tomato fruit ripening factor NOR controls leaf senescence

“…As seen in Figure 6A (and Table S2 is that SlORE1 genes directly control ripening processes in fruits. Similarly, downregulation 433 of NAC transcription factor SlNAP2 expression delays leaf senescence in tomato followed by 434 an increased fruit yield (Ma et al, 2018). SlNAP2 binds to the promoters of several 435 senescence-related genes, including SlSAG113 (Solanum lycopersicum SENESCENCE-436 ASSOCIATED GENE113) and the chlorophyll-degradation genes SlSGR1 (S. lycopersicum 437 senescence-inducible chloroplast stay-green protein 1) and SlPAO (S. lycopersicum 438 pheide a oxygenase).…”

“…suggesting that it has an important function in controlling ABA homeostasis in senescing 441 tomato leaves (Ma et al, 2018). 442…”

Genome-wide analysis of the NAC transcription factor family in broomcorn millet (Panicum miliaceum L.) and expression analysis under drought stress

“…NAC TFs play important regulatory roles in various aspects of plant growth, development, and adaptation to the environment, including in shoot apical meristem formation [5], cell division and expansion [6,7] nutrient remobilization [8], flower formation [9], lateral root development [10,11], leaf senescence [12][13][14][15][16], secondary cell wall biosynthesis [3,[17][18][19][20], fiber development [19,21,22], fruit ripening [23,24], seed development [25], response to pathogen infection [26][27][28][29][30], and abiotic stress tolerance [31][32][33]. Many studies have confirmed that many NAC genes play crucial roles in the regulation of plant tolerance to drought.…”