A small heat shock protein (LhHSP17.9) in cut Lilium ‘Manissa’ flowers alleviates water-loss stress

Small heat shock proteins (sHSPs) are important regulatory factors in plant growth, development, and response to stress. In this study, the regulatory mechanism of the novel lily LhHSP17.9 gene in water-loss stress was investigated by transient silencing and overexpression in Lily (Lilium ‘Manissa’) flower buds and transgenic Arabidopsis thaliana. Transient transformation of Arabidopsis protoplasts revealed that LhHSP17.9 was localized in mitochondria. Expression analysis showed that LhHSP17.9 was highly expressed in leaves, petals, and anthers. Water-loss stress induced the expression of LhHSP17.9, indicating that this gene is involved in the plant's response to dehydration. Under 5 % polyethylene glycol (PEG) 6000 treatment, Lily flowers with LhHSP17.9 - transient silencing exhibited a shorter vase life, higher malondialdehyde (MDA) content, lower activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), and lower transcript levels of LhCu/ZnSOD, LhFeSOD, LhCAT, and LhPOD. In contrast, Lily petals transiently overexpressing LhHSP17.9 showed a delayed browning and reduced relative conductivity. Transgenic Arabidopsis seedlings subjected to mannitol stress had longer root lengths and most plants recovered when the transgenic plants were rehydrated after 15 days. Moreover, the relative expression level of the dehydration-responsive gene (AtDR22) was significantly increased under dehydration stress. In summary, LhHSP17.9 enhances the tolerance of Lily plants to dehydration, primarily by activating the expression of LhCu/ZnSOD, LhFeSOD, LhCAT, LhPOD, and AtDR22 genes.