2.8.2. Transgenic Breeding for Abiotic Stress Resistance

Li et al. generated RNAi transgenic broccoli lines targeting the cellulose synthase gene *BoiCesA*; the *BoiCesA* knockdown plants showed a loss of cellulose content and significantly enhanced salt tolerance, and the expression of related genes (*BoiProH*, *BoiPIP2;2*, *BoiPIP2;3*) was significantly changed but also displayed phenotypic defects characterized by dwarfs and smaller leaves [141].

In three independent studies, Jiang et al. reported that the overexpression of the C3H-type zinc finger genes *BoC3H* and *BoC3H4* and the ethylene response transcription factor gene *BoERF1* enhanced salt stress tolerance [142–144]. The BoC3H-overexpression lines exhibited higher germination rates, dry weight and chlorophyll content under salt stress and less cell death in the leaves due to the decreased hydrogen peroxide level, relative electrical conductivity and malondialdehyde contents but increased free proline content and catalase, peroxidase and superoxide dismutase enzyme activities [142]. The *BoC3H4*-overexpression lines exhibited increased salinity stress tolerance, with an increase in proline and H2O2 and a decrease in chlorophyll loss, MDA and REC compared with WT plants; however, the lines were more susceptible to *S. sclerotiorum*, possibly due to the inhibited expression of the *BoPDF1.2* gene [143]. The *BoERF1*-overexpression lines exhibited a higher seed germination rate and less chlorophyll loss under salt stress, with less cell death in the leaves similar to the *BoC3H*-overexpression lines; in addition, the transgenic lines showed enhanced resistance to *Sclerotinia* stem rot [144].
