add Supplementary Figure 3 caption

assays/qPCR/README.md

+### Supplementary Figure 3 caption
+
+**Supplementary Figure 3:** Cq values of qRT-PCR primer pairs used with dilution series of cDNA.
+Primers for sqs, dxs and rpoA were tested with cDNA extracted after 3 days from *Synechocystis* Δshc
+pEERM Prha sqs pSHDY rhaS, *Synechocystis* Δshc pEERM Prha dxs pSHDY rhaS and Synechocystis
+Δshc pSHDY rhaS, induced with 5 mM rhamnose respectively. Primer sequences are shown in
+Suppl. Table 2.
+
+### Supplementary Figure 3 source
+
+https://www.frontiersin.org/articles/10.3389/fpls.2023.1024981/full#supplementary-material
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