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.

Histone deacetylases (HDACs) mediate histone deacetylation and act in concert with histone acetyltransferases to regulate dynamic and reversible histone acetylation which modifies chromatin structure and function, affects gene transcription, thus, controlling multiple cellular processes. HDACs are widely distributed in almost all eukaryotes, and there have been many researches focusing on plant HDACs recently. An increasing number of HDAC genes have been identified and characterized in a variety of plant species and the functions of certain HDACs have been studied. The present studies indicate that HDACs play a key role in regulating plant growth, development and stress responses. This paper reviews recent findings on HDACs and their functions in plants, especially their roles in development and stress responses.

Heterotrimeric G proteins have been shown to transmit ultraviolet B (UV-B) signals in mammalian cells, but whether they also transmit UV-B signals in plant cells is not clear. In this paper, we report that 0.5 W m 22 UV-B induces stomatal closure in Arabidopsis (Arabidopsis thaliana) by eliciting a cascade of intracellular signaling events including Ga protein, hydrogen peroxide (H 2 O 2 ), and nitric oxide (NO). UV-B triggered a significant increase in H 2 O 2 or NO levels associated with stomatal closure in the wild type, but these effects were abolished in the single and double mutants of AtrbohD and AtrbohF or in the Nia1 mutants, respectively. Furthermore, we found that UV-B-mediated H 2 O 2 and NO generation are regulated by GPA1, the Ga-subunit of heterotrimeric G proteins. UV-B-dependent H 2 O 2 and NO accumulation were nullified in gpa1 knockout mutants but enhanced by overexpression of a constitutively active form of GPA1 (cGa). In addition, exogenously applied H 2 O 2 or NO rescued the defect in UV-B-mediated stomatal closure in gpa1 mutants, whereas cGa AtrbohD/AtrbohF and cGa nia1 constructs exhibited a similar response to AtrbohD/ AtrbohF and Nia1, respectively. Finally, we demonstrated that Ga activation of NO production depends on H 2 O 2 . The mutants of AtrbohD and AtrbohF had impaired NO generation in response to UV-B, but UV-B-induced H 2 O 2 accumulation was not impaired in Nia1. Moreover, exogenously applied NO rescued the defect in UV-B-mediated stomatal closure in the mutants of AtrbohD and AtrbohF. These findings establish a signaling pathway leading to UV-B-induced stomatal closure that involves GPA1-dependent activation of H 2 O 2 production and subsequent Nia1-dependent NO accumulation.