Andrographis paniculata is an important medicinal herb known as a “natural antibiotic”, which has been used in Southeast Asia for thousands of years. The CONSTANS-like (COL) gene is an important regulatory factor for plant photoperiod flowering and stress response. However, there is currently no detailed research on the COL genes of A. paniculata. In our study, we performed a genome-wide analysis of A. paniculata COL (ApCOL) family members using bioinformatics tools and identified nine ApCOL genes. Based on phylogenetic analysis, ApCOLs were categorized into three groups, with members of the same group having similar structures. Gene duplication events indicated that only one pair of duplicated genes was identified, possibly caused by segmental duplication. In terms of evolutionary relationships, the COL proteins of A. paniculata and Sesamum indicum were closely related, showing that they are highly similar in the phylogenetic tree. In addition, ApCOL genes showed tissue specificity and were specifically highly expressed mainly in leaves and flowers. Based on the cis-regulatory element prediction results, we examined the expression levels of ApCOLs under hormone and salt stress, and ApCOL08 was significantly induced. With subcellular localization results consistent with the prediction, we transformed ApCOL08 into yeast and showed significant resistance to salt stress. Our study suggests that ApCOL genes have important roles in response to abiotic stress and plant development and initially identifies key genes for future molecular regulation studies.

Andrographis paniculata is an important medicinal herb known as "natural antibiotic", which has been used in Southeast Asia for thousands of years. CONSTANS-Like (COL) gene is an important regulatory factor for plant photoperiod flowering and stress response. However, there is currently no detailed research on the COL genes of A. paniculata. In our study, a systematic analysis of A. paniculata COL (ApCOL) family members was performed, and a total of 9 ApCOLs were identified, which were renamed according to their position order on the chromosomes. They were divided into three groups by phylogenetic analysis, with group II being the group with the most COL genes among the six dicotyledonous plants and all eight species. The results of gene duplication events showed that the evolution of ApCOLs in A. paniculata were conservative, with only one pair of segmental duplication genes, belonging to group II, as the main driving force of evolution. In addition, expression profiles of 9 ApCOL genes in five tissues were analyzed by RNA-seq, displaying their tissue-specific expression. Their expression levels under hormone and salt stress were analyzed by qRT-PCR, and the strongly induced ApCOL08 was selected as the key gene, and its potential biological function in resisting salt stress was revealed by heterologous expression of this gene in yeast. Our research implies that the ApCOL genes have essential functions in response to abiotic stresses and plant development, and has preliminarily identified the key genes for further research in molecular regulation in the future.