Expression analysis of tiller-related genes during axillary bud outgrowth in ratoon rice

【Objective】The expression of tiller-related genes during axillary bud outgrowth in ratoon rice were profiled to provide insight into the molecular mechanisms underlying axillary bud development in the ratoon season.【Method】The rice varieties i21 and i89 with high and low ratooning abilities, respectively, were used as the study materials. Real-time fluorescence quantitatire PCR(qRFRCR) was used to characterize the expression dynamics of eight tiller-related genes at the stages of tiller initiation, elongation and booting of the first season and at 1, 24, 48 and 72 h after heading removal in the ratoon season. The correlation between tiller-related genes and maximum ratoon tillers was analyzed and the genes with high correlation with axillary bud growth were selected.【Result】The number of ratoon tillers in i21 and i89 increased gradually with the growth of axillary buds and reached a stable maximum 20 d after the first-season harvest. However, i21 ratoon tillers grew much faster than those of i89 and the maximum number of ratoon tillers of i21 and i89 were 33 and 10, respectively. The relative expression levels of LAX1, LAX2 and MOC1 genes differed significantly in the two varieties. The relative expression levels of LAX1, LAX2 and MOC1 genes in i21 were significantly higher than those in i89 during the ratooning period(P < 0.01, the same below). MOC1 reached peak levels at 1 h after beheading, whereas the expressions of LAX1 and LAX2 peaked at 24 h after beheading then decreased significantly(P < 0.05, the same below) to stable levels thereafter. During ratooning, the relative expression levels of D10, HTD1, OsTB1 and TAD1 genes in i89 were significantly higher than those in i21, except for TAD1 at 24 h after beheading. D10 and HTD1 genes peaked at 1 h after beheading, while OsTB1 and TAD1 genes reached their peak values later at 24 and 48 h after beheading. The relative expression levels of D27 in i21 and i89 increased initially but decreased at 24-72 h after heading removal, although this decrease in i21 was significantly less than that in i89. The maximum tiller number was positively and significantly correlated with the expression levels of LAX2 and MOC1 and negatively correlated with those of D10, HTD1, OsTB1 and TAD1. In addition, different gene expression levels also had different correlations.【Conclusion】The high expression of LAX1, LAX2 and MOC1 genes was beneficial to the formation of ratoon tillers, while the high expression of D10, HTD1, OsTB1 and TAD1 genes inhibited ratoon till outgrowth. This work indicates that the different tiller-related genes interacted to jointly regulate ratoon tiller formation.