*2.4. Vector Construction and Subcellular Localization of Sl1*

The full length CDS of *Sl1* were amplified with primers (Forward primer 5 -CTCTCGA-GCTTTCGCGAGCTCATGGATCTTGTTAGACTAAAGTATTTTGAA-3 , Reverse primer 5 - GCCCTTGCTCACCATGGATCCTGACTCTAACTGAATAGGTAAAACTACATTTC-3 ), and the PCR products were inserted into *Sac*I and *BamH*I site of pCAMBIA2300 with a GFP tag at the C terminus. The primers were designed by homologous recombination methods as described previously. After confirming positive clones by sequencing, the vector (35S-*Sl1*-GFP) and empty vector were transformed into *A. tumefaciens* strain GV3101. Transgenic *Nicotiana benthamiana* that expressed with nucleus-located signaling (RFP-H2B) was used for transient expression. The transient expression method was described previously [37]. For the fluorescence image acquisition, a Nikon A1 confocal microscope (Nikon, Tokyo, Japan) was used at 48 h post infiltration in tobacco leaves, and the excitation/emission wavelengths of GFP were 488 nm/480–520 nm, and the excitation/emission wavelengths of RFP were 561 nm/610–630 nm.

#### *2.5. Measurement of Actual Quantum Efficiency of PSII Photochemistry*

After 15 d treatment of Cd, plants were dark-adapted for 30 min before measurement. The actual quantum efficiency of PSII photochemistry (ΦPSII) was determined by the Imaging PAM (IMAG-MAXI, Heinz Walz, Germany) in the fifth fully expanded leaves as described previously [38].

#### *2.6. Measurements of Hydrogen Peroxide and Antioxidants Enzyme Activity*

Three-tenths gram of tomato root samples were collected and ground in liquid nitrogen. The samples were combined with 3 mL precooled 1 M HClO4 in a 10 mL centrifuge tube and mixed thoroughly. The pH of the sample was adjusted to 6–7 using 4 M KOH, 0.05 g activated carbon was then added to absorb pigments. The samples were centrifuged at 12,000× *rpm* for 10 min at 4 ◦C and supernatants were collected in 5 mL tubes for reaction. The reaction buffer was as follows: 1 mL supernatant or H2O2, 996 μL 1 mM ABTS (dissolved in 100 mM potassium acetate, pH 4.4), and 4 μL POD (P8375, Merck KGaA, Darmstadt, Germany). The absorbance of reaction buffer was detected at a wavelength of 412 nm by a SHIMADZU UV-2410PC spectrophotometer (Shimadzu Company, Kyoto, Japan) and the content of H2O2 was calculated by a standard curve [39].

Three-tenths gram fresh tomato roots were ground in liquid nitrogen and dissolved in a precooled buffer that included 50 mM phosphate buffered saline (pH 7.8), 0.2 mM EDTA, 2 mM ascorbic acid, and 2% (*w*/*v*) poly-vinylpolypyrrolidone. The samples were mixed thoroughly using vortex and then centrifuged at 12,000× *g* for 20 min at 4 ◦C. The supernatant was collected in new centrifuge tubes for detecting enzyme activity. The method of measuring enzyme activities of SOD, CAT, APX, and GR was described previously [40].

#### *2.7. Measurement of Cd Content and Cd Localization*

Tomato leaves and roots were washed and collected in liquid nitrogen after 10 d Cd treatment. Samples were put in the oven for 30 min at 115 ◦C then transferred to 60 ◦C for total dryness. The dried sample was ground and mixed with an acid solution that contained HClO4 and HNO3 (1:3, *v*:*v*). The samples were digested at 180 ◦C and the solution was then evaporated to 1-2 mL for dilution. The remained solution was diluted with deionized water to a final volume of 50 mL and inductively coupled plasma mass spectrometry (ICPMS-2030, Shimadzu Company, Kyoto, Japan) was used for determining Cd content [25].

For Cd localization, the LeadmiumTM Green AM probe (Invitrogen, Carlsbad, CA, USA) was used for Cd staining according to the manufacturer's instructions. The root tips were stained by immersing in dye solution for 3 h in dark at room temperature; the sample

was then washed three times with buffer (0.85% NaCl). A Nikon A1 confocal microscope (Nikon, Tokyo, Japan) was used to detect the Cd localization, and the excitation/emission wavelengths of GFP were 488 nm/510–530 nm [41]. The mean fluorescence intensity values of Cd stained root tips were detected by ImageJ 1.53 analysis software (National Institute of Health, Bellevue, WA, USA) and relative fluorescence intensity normalized to the intensity of the wild-type group under Cd stress.

#### *2.8. Total RNA Isolation and qRT-PCR Analysis*

One-tenth gram tomato samples were collected in a 2 mL centrifuge tube and frozen in liquid nitrogen. An RNAprep pure plant kit (Tiangen Biotech, Beijing, China) was used for total RNA extraction according to the manufacturer's instructions. Five-tenths milligram total RNA was used to reverse transcribe to cDNA template by HiScript II Q RT SuperMix for qPCR Kit (Vazyme, Nanjing, China). qRT-PCR was conducted with ChamQ Universal SYBR qPCR Master Mix (Vazyme, Nanjing, China) on a Light Cycle 480 II Real-Time PCR detection system (Roche, Basel, Switzerland). The total 20 μL reaction system was as follows: 10 μL SYBR qPCR Master Mix, 1 μL cDNA template, 10 μM forward and reverse primer, and deionized water. The PCR program was performed with 30 s at 95 ◦C, followed with 35–40 cycles of 10 s at 95 ◦C, 30 s at 58 ◦C, and 1 min at 72 ◦C. *ACTIN* was used for calculating the relative expression level of the target gene. The primers are listed in Table S1.
