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

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.