Effects of P<sub>SAG12</sub><italic>-IPT </italic>gene expression on leaf senescence, yield, and fiber quality in cotton

Abstract

<p indent="0mm">A chimeric gene of bacterial <italic>IPT</italic> and the senescence-specific SAG12 promoter from <italic>Arabidopsis</italic> (P_SAG12-<italic>IPT</italic>) was overexpressed in cotton, and nine independent transgenic lines were obtained. To identify the leaf senescence characteristics, yield, and fiber quality of P_SAG12-<italic>IPT</italic> cotton plants, we performed the experiments at the Shangzhuang Experimental Station of China Agricultural University in 2011 and 2012. The results showed that the expression of <italic>IPT</italic> genes in transgenic lines was dramatically up-regulated at leaf aging stage, and the content of Z+ZR-type cytokinin was significantly higher than that of wild type Jihe 321. According to the content of Z+ZR-type cytokinin, nine transgenic lines were clustered into three categories with strong, weak, and moderate anti-aging ability. During leaf senescence period, the contents of chlorophyll and soluble proteins in transgenic lines were positively related to the content of Z+ZR-type cytokinin. Compared to wild type, transgenic lines had a higher or equal number of bolls (diameter ≥ <sc>2 cm)</sc> per plant and boll weigh, but their boll-opening rate at the first harvest was significantly decreased, and the extent of reduction was positively related to the anti-aging ability. Consequently, the seed cotton yield of P_SAG12-<italic>IPT</italic> lines (<italic>OE</italic>-37 and <italic>OE</italic>-38) with strong or moderate anti-aging ability decreased due to less opened bolls, while the line (<italic>OE</italic>-30) with weak anti-aging ability had a comparable yield to that of wild type. The fiber length uniformity of P_SAG12-<italic>IPT</italic> cotton lines was significantly higher than that of wild type. Compared with wild type, the micronaire results of transgenic lines revealed an increasing trend, and fiber length, breaking strength, and breaking elongation was not significantly different from that of wild type.