Effect Of Stigma Ca²⁺ Levels On Self-incompatibility In Chinese Cabbage

Self-incompatibility（SI）is a genetic mechanism to promote outcrossing and prevent self-fertilization in plants.Brassicaceae crops have a typical SI response that the pollen can not germinate or the pollen tube can not pass through the stigma into the style to complete fertilization.Calcium(Ca²⁺)is a necessary regulator of pollen germination and pollen tube growth,and cytoplasmic Ca²⁺levels can affect pollen germination and pollen tube growth during SI response.However,the signaling processes of Ca²⁺regulating the SI response are not clear in Chinese cabbage.In this study,exogenous CaCl₂and EGTA was sprayed to alter the Ca²⁺level of the stigma,observe pollen germination and pollen tube growth,and detect the correlation between Ca²⁺and SI response in Chinese cabbage.The main results are as follows:1.The determination of flowering compatibility index in 10 Chinese cabbage inbred lines showed that‘91-125’had strong self-incompatibility with the flowering compatibility index of 0.18,and‘14S23’had strong self-compatibility with the flowering compatibility index of 24.33.Observation of Chinese cabbage pollen germination and pollen tube growth in vivo after pollination during the flowering period verified that the Chinese cabbage‘91-125’is a typical strong self-incompatible line（SI line）and‘14S23’is a typical strong self-compatible line（SC line）.2.After treating the stigma of Chinese cabbage with different concentrations of CaCl₂and EGTA,it was found that the decrease in Ca²⁺levels in the stigma of‘91-125’could promote pollen germination and break the SI response,and the increase in Ca²⁺levels in the stigma of‘14S23’could inhibit pollen germination.3.Observation of transmission electron microscopy showed that a large amount of Ca²⁺precipitation accumulated on the stigma of‘91-125’when the SI response occurred,while there was only a small amount of Ca²⁺distribution on the stigma of‘14S23’during the SC response,indicating that the Ca²⁺level of the stigma may be related to the occurrence of SI response.4.A total of 8 BrCaM and 9 BrCAMTA family genes were identified in Chinese cabbage by genome-widely analysis.After self-pollination,the expression changes of BrCaM and BrCAMTA family genes were analyzed in the stigma treated with EGTA and CaCl₂.The results of expression analysis showed that the expression of multiple BrCaM and BrCAMTA genes was consistent with the changes of stigma Ca²⁺level and the SI responses,which suggests that BrCaM and BrCAMTA genes may be involved in regulating pollen germination and pollen tube growth.