The roles of a tomato （Lycopersicon esculentum） chloroplast-targeted DnaJ protein （LeCDJ1） were investigat-ed using wild-type （WT） and sense transgenic tomatoes. The LeCDJ1 expression was upregulated by 38℃, 42 ℃, 45 ℃, NaCl, PEG, methyl viologen （MV） and hydrogen peroxide （H2O2）, but not by 30 ℃ and 35 ℃. Meanwhile, LeCDJ1 was involved in the response of plants to abscisic acid （ABA）. Under heat stress, the sense plants showed better growth, higher chlorophyll content, lower malondialdehyde （MDA） accumulation and relative electrical conductivity （REC）, and also less PSII photoinhibition than WT. Interestingly, the sense plants treated with streptomycin （SM）, an inhibitor of organellar translation, still showed higher maximum photo-chemistry efficiency of PSII （Fv/Fm） and D1 protein levels than the SM-untreated WT, suggesting that the protective effect of LeCDJ1 on PSII was, at least partially, independent of D1＆amp;nbsp;protein synthesis. Furthermore, the relatively lower super-oxide radical （O2^＊-） and H2O2 levels in the sense plants were considered to be due to the higher ascorbate peroxidase （APX） and superoxide dismutase （SOD） activity, which seemed unlikely dependent on their transcription level. These results indicated that LeCDJ1 overexpression facilitated heat tolerance in transgenic tomatoes.
SUMOylation is an impo^ant post-translational modification process that regulates different cellular functions in eukaryotes. SIZ/PIAS-type SAP and Mizl （SIZ0 proteins exhibit SUMO E3 ligase activity, which modulates SUMOylation. However, SIZI in tomato has been rarely investigated. In this study, a tomato SIZI gene （SISIZI） was isolated and its molecular characteristics and role in tolerance to drought stress are described. SISIZI was upregulated by cold, sodium chloride （NaCI）, polyethylene glycol （PEG）, hydrogen peroxide （H20~） and abscisic acid （ABA）, and the corresponding proteins were localized in the nucleus. The expression of SISIZI in Arabidopsis thaliana （Arabidopsis） sizl-2 mutants partially complemented the phenotypes of dwarf, cold sensitivity and ABA hypersensitivity. SISIZI also exhibited the activity of SUMO E3 ligase to promote the accumulation of SUMO conjugates. Under drought stress, the ectopic expression of SISIZl in transgenic tobacco lines enhanced seed germination and reduced the accumulation of reactive oxygen species..SISIZl overexpression conferred the plants with improved growth, high free proline content, minimal malondialdehyde accumulation and increased accumulation of SUMO conjugates. SISIZ1 is a functional homolog of Arabidopsis SIZ1 with SUMO E3 ligase activity. Therefore, overexpression of SISIZ1 enhanced the tolerance of transgenic tobacco to drought stress.
Song ZhangKunyang ZhuangShiju WangJinlian LvNa'na MaQingwei Meng
