Identification Of Heat Tolerance And SmAPX2 Response To High Temperature Stress In Eggplant At Seedling Stage

Eggplant（Solanum melongena L.）is a popular vegetable in China,with the highest production volume in the world.With the exacerbation of global warming,eggplant production will be greatly affected.High-temperature stress causes damage to plants,including accelerated chlorophyll decomposition in leaves,hindered dark reactions of photosynthesis,yellowing of leaves,and appearance of necrotic spots;decreased pollen viability,burned fresh fruits,increased malformed fruits,and decreased fruit quality;accumulation of reactive oxygen species,damage to membrane permeability,and reduced nutrient growth,seriously reducing economic benefits.In this study,we identified two germplasms with different levels of high-temperature tolerance during the seedling stage of eggplant,namely the high-temperature tolerant variety ’AC013’ and the heat-sensitive variety’14C-17’.To investigate the role of ascorbate peroxidase（APX）in the process of eggplant resistance to high temperature stress,we identified nine members of the SmAPX family and examined their expression levels under high-temperature stress using quantitative real-time PCR（qRT-PCR）.SmAPX2 was significantly up-regulated in eggplant under high-temperature stress.Using subcellular localization,tobacco transient overexpression,and gene silencing experiments,we studied the role of SmAPX2 in eggplant’s resistance to high-temperature stress.The main results are as follows:In this study,we evaluated the heat tolerance of eggplant at seedling stage using 20 germplasms preserved in the laboratory.The results showed that ’AC013’ is a heat-tolerant material,while ’14C-17’ is a heat-sensitive material.To determine the physiological indicators of these two materials under high temperature stress,we measured the chlorophyll content,soluble sugar content,malondialdehyde（MDA）content,proline（PRO）content,hydrogen peroxide（H₂O₂）content,catalase（CAT）activity,and ascorbate peroxidase（APX）activity.The results showed that the chlorophyll content of eggplant leaves decreased under high temperature stress,with ’AC013’ showing a smaller decrease than ’14C-17’.The soluble sugar content,MDA content,H₂O₂ content,CAT activity and APX activity were upregulated in the early stages of high temperature treatment,with ’AC013’ showing lower increases in soluble sugar content,MDA content,and H₂O₂ content than ’14C-17’,but higher increases in PRO content,CAT activity,and APX activity.Subsequently,we identified the members of the SmAPX gene family in eggplant.Nine members of the SmAPX gene family were identified,including two cytoplasmic SmAPX3c and SmAPX6,five peroxisomal SmAPX3a,SmAPX3b,SmAPX1a,SmAPX1b and SmAPX2,and two chloroplast mitochondrial SmsAPX and SmtAPX.Bioinformatics analysis revealed that most of these nine members contain cis-acting elements related to stress response.We analyzed the expression patterns of these genes under high temperature stress,and the results showed that the relative expression level of SmAPX2 was significantly upregulated in eggplant under high temperature stress,reaching its peak at 2 hours of treatment with a 30-fold increase in expression.To further verify the gene function of SmAPX2,subcellular localization experiments showed that SmAPX2 functions in the cytoplasm,which is consistent with the predicted peroxisomal subtype of SmAPX2.Transient overexpression of SmAPX2 in Nicotiana benthamiana leaves reduced the accumulation of H₂O₂.Virus-induced gene silencing（VIGS）experiments showed that the silenced eggplant plants had more severe wilting symptoms compared to the control group,with a greater accumulation of H₂O₂ and a significant decrease in APX enzyme activity.These results indicate that SmAPX2 can improve the heat tolerance of eggplant by reducing cell membrane lipid peroxidation damage through the removal of H₂O₂.