Characterizing the HMA gene family in dragon fruit (Selenicereus undatus L.) and revealing their response to multifactorial stress combinations and melatonin-mediated tolerance.

• HuHMA gene family exhibited unique expression patterns in the growth and development of pitaya. • Transcriptome analysis revealed that HMA-1/11//18/19/28/29 genes exhibited significantly higher expression in single and combined multifactorial stresses. • Comprehensive genome-wide characterization and expression profiling revealed the diverse role of HMA gene members under abiotic stresses and melatonin-mediated tolerance in pitaya. • Exogenous application of melatonin mitigates the effect of combined stresses and HMA gene family members exhibited significantly higher expression. Plants have evolved various ways to improve their tolerance against heavy metal stress including physiological, biochemical, and molecular pathways. The heavy metal-associated (HMA) gene family plays an important role in the detoxification of metal ions. Research on HMA protein diversification, expression, and function in S. undatus is limited. In this study, we have identified 29 HMA proteins andrenamed them as HuHMA-1 to HuHMA-29. Our genome-wide characterization analysis supports the classification of HuHMA gene family members into 11 subfamilies based on their phylogenetic tree topology and conserved motif domains. RNA-Seq analysis exhibited varied expression in pitaya tissues at different developmental stages where we found HuHMA-1 & 16 gene family members strongly expressed in flower buds, flower, pericarp and pulp. Duplication event and Ka/Ks ratio depict that most of the HuHMA genes are generated by segmental duplication, except two pairs of the genes (HuHMA18-HuHMA20 and HuHMA28-HuHMA29) originated through proximal duplication mapped on Chr07 and Chr11. Transcriptome analysis of single and multifactorial stress-treated plants revealed candidate genes (HMA-1/11/18/19/28/29) that might play diverse functions to ameliorate the impact of heavy metal stresses individually and the combined effect of heat and drought. These HMA gene family members exhibited significantly higher expression under multifactorial stresses. The present analysis provides a theoretical foundation for the functional study through advanced biotechnological tools and provides novel insight into the structure and evolution of the HuHMA genes. [ABSTRACT FROM AUTHOR]