Candidate reference genes for quantitative gene expression analysis in Lagerstroemia indica

Quantitative gene expression analysis by qPCR requires reference genes for normalization. Lagerstroemia indica (crape myrtle) is a popular ornamental plant in the world, but suitable endogenous reference genes are lacking. To find suitable reference genes, we evaluated the stabilities of nine candidate genes in six experimental data sets: six different tissues, three leaf colors, nine flower colors, and under three abiotic stresses (salt, drought, cold) using four statistical algorithms. A target gene LiMYB56 (homolog of Arabidopsis MYB56) was used to verify the authenticity and accuracy of the candidate reference genes. The results showed that the combination of two stably expressed reference genes, rather than a single reference gene, improved the accuracy of the qPCR. LiEF1 alpha-2 + LiEF1 alpha-3 was best for the tissue, salt treatment, and drought treatment sets; LiEF1 alpha-2 + LiEF1 alpha-1 was optimal for leaf color; LiEF1 alpha-2 + LiACT7 was optimal for cold treatment; and LiUBC + LiEF1 alpha-1 was best for the flower color set. Notably, LiEF1 alpha-2 had high expression stability in all six experimental sets, implying it may be a good reference gene for expression studies in L. indica. Our results will facilitate future gene expression studies in L. indica.