UPR induction during legume‐rhizobia symbiosis. a,b) Fluorescent quantitative PCR detection of spliced MtbZIP60 (sMtbZIP60) (a) and MtBIP3 mRNA (b) in early symbiosis (0, 24, 48h post‐inoculation, pi). c) Relative expression levels of sMtbZIP60 and MtBIP3 genes in multiple organs of the same plant. d–f) Relative expression levels of MtIRE1A (d), MtIRE1B (e), and MtbZIP60 (f) along the symbiotic process are represented by distinct nodule sections. Zone I (meristematic), zone IId (distal) and zone IIp (proximal) constitute zone II (infection and differentiation zone). The data were obtained from the Symbimics website, curated from a previous publication,[³⁸], and represent the means of three technical replicates. Individual data points are not available. g‐i) Nodules at 14 dpi were dissected from M. truncatula transgenic lines expressing the β‐glucuronidase (GUS) reporter under the control of promoters of MtIRE1A (g), MtIRE1B (h) and MtbZIP60 (i) respectively and stained with GUS solution for semi‐section. Ruthenium red staining was performed for imaging. Scale bars = 0.1 mm. For (a–c), all data are shown as mean ±SD. n = 3, ****p < 0.0001 versus mock sample (a, b) and other organs (c). The statistical analysis was performed using the unpaired two‐sided Student's t‐test in (a, b) and ANOVA with post‐hoc comparisons in (c‐f). The letters indicate values with statistically significant (p < 0.05) and non‐significant (p > 0.05) differences, respectively.