INVESTIGATING PLANT SENESCENCE: THE ROLE OF NAC TRANSCRIPTION FACTORS IN SOLANUM LYCOPERSICUM AND ARABIDOPSIS THALIANA

THESIS OUTLINE In the present thesis work, the senescence process in fruit and leaf has been investigated through the analysis of different mutant lines of Arabidopsis thaliana and Solanum lycopersicum. In particular, the work has focused on the downregulation of three NAC transcription factor genes, NAC058 (AT3G18400), NAC100 (AT5G61430, both analysed in Arabidopsis), and HEBE (Solyc12g036480), analysed in tomato. All of them have been selected for the analysis due to their putative role in senescence, e.g. their expression has been detected in senescing siliques (NAC058, NAC100) and in ripening berries (NAC100). In addition, HEBE is the putative ortholog in tomato of NAC058 of Arabidopsis. The work has been divided in the following chapters: - CHARACTERIZATION OF NAC058, A NEGATIVE SENESCENCE REGULATOR IN SILIQUES OF Arabidopsis thaliana - in this section, NAC058 is identified as fruit-specific negative regulator of senescence. Overexpression lines are analysed and NAC058 expression is localized in different tissues of 21 the siliques. Moreover, the bond between this transcription factor and phytohormones is preliminarly evaluated. - NAC100, A NOVEL NAC TRANSCRIPTION FACTOR THAT NEGATIVELY REGULATES FRUIT SENESCENCE IN Arabidopsis thaliana – in this chapter, a comparison between transcriptomic data of Arabidopsis senescing siliques and tomato ripening berries allows to identify conserved NAC genes expressed during fruit maturation. 7 Arabidopsis lines carrying T-DNA insertions in these genes are analysed looking at senescence-related traits and, among them, nac100 is selected as putative negative regulator of silique senescence. In addition, NAC100 is found to affect silique development. - HEBE, A NOVEL POSITIVE REGULATOR OF LEAF SENESCENCE IN Solanum lycopersicum – in this section, HEBE, the putative ortholog of NAC058 in tomato, is temporary silenced in tomato plants through Virus-Induced Gene Silencing (VIGS), resulting in a stay-green phenotype. The work has been published in 2020 (paper in attachment at the chapter).