OsMT2b Regulates Pollen Development and ROS Homeostasis in a Photoperiod-Dependent Manner

Reactive oxygen species (ROS) are signalling molecules that promote programmed cell death in animal and plant systems. However, their role in rice (Oryza sativa L.) anther development is unclear. In this study, we show that lower transcript levels of the metallothionein gene OsMT2b in japonica rice plants obtained by RNA interference (RNAi) resulted in a serious reduction in the seed setting rate. Observations of semi-thin sections of anthers indicated that tapetum degradation initiates early and ends late in OsMT2b-RNAi plants relative to the wild type (WT). Nitroblue tetrazolium staining and measurements of hydrogen peroxide contents showed that ROS contents are higher in OsMT2b-RNAi plants than in WT. Terminal-deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assays showed that abnormal programmed cell death in the tapetum results in sterile microspores. In addition, the OsMT2b-RNAi plants were sensitive to photoperiod; they were sterile under natural long-day conditions but almost fully fertile under natural short-day conditions, indicating that OsMT2b integrates photoperiod information into pollen development. The discovery of this rice material may enrich germplasm resources for two-line hybrid rice breeding, and further research may enable its application in two-line hybrid rice breeding.