CONSTANS (CO) is an important regulator of photoperiodic flowering and functions at a key position in the flowering regulatory network. Here, two CO homologs, MiCOL16A and MiCOL16B, were isolated from “SiJiMi” mango to elucidate the mechanisms controlling mango flowering. The MiCOL16A and MiCOL16B genes were highly expressed in the leaves and expressed at low levels in the buds and flowers. The expression levels of MiCOL16A and MiCOL16B increased during the flowering induction period but decreased during the flower organ development and flowering periods. The MiCOL16A gene was expressed in accordance with the circadian rhythm, and MiCOL16B expression was affected by diurnal variation, albeit not regularly. Both the MiCOL16A and MiCOL16B proteins were localized in the nucleus of cells and exerted transcriptional activity through their MR domains in yeast. Overexpression of both the MiCOL16A and MiCOL16B genes significantly repressed flowering in Arabidopsis under short-day (SD) and long-day (LD) conditions because they repressed the expression of AtFT and AtSOC1. This research also revealed that overexpression of MiCOL16A and MiCOL16B improved the salt and drought tolerance of Arabidopsis, conferring longer roots and higher survival rates to overexpression lines under drought and salt stress. Together, our results demonstrated that MiCOL16A and MiCOL16B not only regulate flowering but also play a role in the abiotic stress response in mango.
CONSTANS/CONSTANS-like (CO/COL) transcription factors play a vital role in the photoperiodic flowering pathway. However, the biological functions of COL genes in mango are unclear. In this study, we identified 31 COL genes from the ‘Jin Huang’ mango genome and divided them into three groups according to the specific gene structure and protein domain characteristics. These 31 MiCOL genes were heterogeneously distributed on 14 chromosomes. Expression pattern analysis showed that most MiCOL genes were mainly expressed in leaves and stems and during the floral induction period, followed by the floral differentiation period. The expression of COL genes was induced by drought and salt stress, but the expression patterns of different genes were different, which may suggest that MiCOL genes are involved in the abiotic stress response of mango. Under salt and drought conditions, two MiCOL9 genes can improve the resistance of Arabidopsis by improving the scavenging ability of ROS and proline accumulation and reducing the MDA content. Additionally, overexpression of MiCOL9 genes significantly inhibited flowering in transgenic Arabidopsis. This work provides an important foundation for understanding the biological roles of mango COL genes in plant growth, development and stress responses.
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