The transcription factor SlPLATZ22 negatively regulates salinity tolerance in tomato plants

The PLATZ (Plant AT-rich sequence and zinc-binding protein) family of transcription factors plays a critical role in plant growth, development, and stress responses. Previous work identified SlPLATZ22 as a salt-responsive gene in tomato plants, but its precise function remained unclear. This study aimed to elucidate the biological function of SlPLATZ22 in regulating salt tolerance in tomato. Following 200 mM salt treatment, the expression of SlPLATZ22 was significantly upregulated in the roots, stems, leaves, flowers, and red-ripe fruits of salt tolerant 'LA1598' and salt-sensitive 'Ke feng' genotypes. SlPLATZ22 was further found to localize in the nucleus. Interestingly, SlPLATZ22 knockout lines (SlPLATZ22#KO) were more tolerant to salt stress than wild type (WT) and SlPLATZ22 overexpression lines (SlPLATZ22#OE), suggesting that SlPLATZ22 functions as a negative regulator of the salt stress response. Compared with the SlPLATZ22#KO, hydrogen peroxide (H₂O₂) content and superoxide anion (O₂^·-) production rates significantly increased in the WT and SlPLATZ22#OE with obvious leaf chlorosis and oxidative damage. In contrast, the antioxidant enzyme activities, as well as proline (Pro) and soluble protein (SP) contents, were significantly higher in the SlPLATZ22#KO. These enhanced plants' ability to scavenge reactive oxygen species (ROS) to reduced oxidative damage, and thereby protected cell membranes and protein stability. In agreement, malondialdehyde (MDA) levels and cell injury in the WT and SlPLATZ22#OE were significantly higher than SlPLATZ22#KO. Altogether, SlPLATZ22 negatively regulated salt tolerance in tomato plants. Our study helps to dissect the molecular regulation mechanism of SlPLATZ22 and provides important genetic resources for breeding salt-tolerant varieties.