Fig. 6: Thermotolerance level of kiwifruit species correlates with the presence of a GATA-box in their respective EGY3 promoters.

a Genotyping of the GATA-box natural variation in different species of kiwifruit by PCR using a forward primer targeting the GATA-Box and a reverse primer targeting the CDS of EGY3. RZ: Ruan Zao (A. arguta); JT: JinTao (A. chinensis); ML: MiLiang (A. deliciosa); HT: White (A. eriantha). Shoot phenotypes (b), leaf survival rates, and EGY3 expression levels detected by qRT-PCR (c) of a range of kiwifruit species before and after heat stress treatment. d Genotyping of the natural variation in several wild-type lines of MH (A. eriantha). e, f Shoot phenotypes (e), leaf survival rates, and EGY3 expression levels of MH-Z11 and JX02 (A. eriantha) before and after heat stress treatment. g Interactions between AeGATA1 and AeHSFA2-2 with the EGY3 promoter of MH-JX02 (proEGY3^JX02) were analyzed by dual-luciferase reporter assays in tobacco leaves. The quantitative analysis of their interaction was performed by LUC/REN measurements. EV empty vector. In (c, f, g), data represent mean ± SD (n = 3 biological replicates). Different lowercase letters indicate statistical significance at p < 0.05 by one-way ANOVA with Duncan’s multiple-range test. Asterisks indicate significant differences by two-tailed Student’s t-test (**p < 0.01, ***p < 0.001). “ns” indicates no statistically significant difference. h Proposed model providing a molecular explanation for the thermotolerance differences between HY0809 and MH-Z11. In both MH-Z11 and HY0809, the respective AeHSFA2−2 and AcHSFA2-2 transcription factors mediate the heat stress induction of AeEGY3 and AcEGY3. In HY0809, however, AcGATA1 further elevates AcEGY3 expression because of the presence of a GATA-box in the AcEGY3 promoter, which is absent in AeEGY3. As a result, HY plants accumulate more EGY3, possibly interacting with CSD2 to lead to more H₂O₂ production in chloroplasts. Increased H₂O₂ accumulation promotes the oligomerization of AcHSFA2-2 and its transcription activity, resulting in higher expression levels of its target genes, such as EGY3 and HSP70−2, which are required for thermotolerance. Source data are provided as a Source Data file.