Fig. 6: HB21 represses the expression of several pollen-wall-related genes.

a cis-elements of the potential HB21 binding sites on the CalS5, RPG1/SWEET5, CYP703A2 and NST2 promoters. b the results of gel shift analysis showed that HB21 can directly bind to the probes on the CalS5, RPG1/SWEET5, CYP703A2 and NST2 promoters. c ChIP analyses of the direct binding of HB21 to the potential binding sites on the promoter of the downstream genes (CalS5, RPG1, CYP703A2, NST2) in the p35S:HB21-GFP line. The probe on the β-TUBULIN promoter was used as a negative control. Data are presented as mean values +/- SD. The error bars represent the SDs from three independent biological repeats. Student’s t test was used for statistical analysis of the difference between the wild type and mutants, ns, no significant difference, *p < 0.05, **p < 0.01, ***p < 0.001 (p-values are shown in the figure). d tobacco transient expression assay for luciferase activity detection. The results showed that HB21 could repress the expression of CYP703A2, RPG1/SWEET5 and NST2. e the working model shows that HB21 globally regulates pollen wall pattern establishment (in pollen mother cells), sporopollenin material synthesis (in the tapetum) and endothecium lignification (in the endothecium) by regulating the expression of CalS5, RPG1/SWEET5, CYP703A2 and NST2.