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The MADS29 gene regulates the plumpness of rice seeds and affects seed development by regulating the degradation of maternal tissues and maintaining the plants hormone balance. Rice seeds produced by heteroploid crosses exhibit greater rate of sterility than that by seeds of other plants. To determine whether MADS29 and its related genes regulate seed development, we used four rice cultivars (two diploid and two tetraploid) to produce four self-crossed combinations as the control and eight hybridized combinations as reciprocal crosses. Then, pollen grain fertility, pollen germination, and seed development were observed, and the expressions of MADS29 and related genes were quantified using RT-PCR. The results showed the following: (1) heteroploid crosses showed 100% successful fertilization, with non-negligible rate of seed abortion. (2) Based on examinations of paraffin sections of seeds at 3 days after pollination (3 DAP) in a 4 n ×2 n cross, the endosperm had entered the cellularization stage, but the number of cells was lower than that in the control. However, in the endosperm of seeds of 2 n ×4 n crosses, the cell walls did not form around the nucleus. In addition, some vacuolation was noted in the endosperm, and cellularization was delayed. (3) qRT-PCR results showed that the relative expression levels of MADS29 , IAA , and programmed cell death (PCD) genes associated with maternal tissues in hybrid seeds at 6 DAP and 8 DAP were significantly higher than those of the control. On the contrary, the relative expression of starch synthesis genes in hybrid seeds was significantly lower than that of the control. This suggests that MADS29 is more highly expressed in the seeds of heteroploid crosses. In addition, it suggested that the expressions of IAA and other genes involved in the PCD of maternal tissues was upregulated in the same seeds. However, starch synthesis genes showed downregulated expression levels, leading to the abnormal development of the endosperm, followed by seed abortion. Thus, high expression of MADS29 leads to hybrid seed abortion, a novel regulatory pattern that is not observed in diploid rice seeds. |
