Disruptions of sugar utilization and carbohydrate metabolism in rice developing anthers aggravated heat stress-induced pollen abortion.

High temperature (HT) stress at reproductive stage is one of most important environment negatively affecting spikelet fertility and rice yield. In this study, the effect of HT exposure on the sugar composition and carbohydrate metabolism in developing anthers and its relation to floret fertility and pollen viability were investigated by different temperature regimes under well-controlled climatic condition. Result showed that HT exposure during microspore development significantly reduced the starch deposition in developing anther and evidently disrupted the spatial distribution of sugar and starch concentrations in different compartments of rice anther, with the higher ratio of sucrose to hexose concentrations in HT-stressed anthers relative to the control ones. Under HT exposure, the amount of starch deposition in the fraction of sporophytic tissues dropped evidently, while the concentrations of sucrose and starch in anther wall tissue enhanced significantly, suggesting that HT exposure impaired the translocation of sucrose from the anther wall tissue to the sporophytic tissues inside rice anther. Furthermore, we presented possible contribution of various genes and key enzymes involving in sugar conversion and carbohydrate metabolism in developing anther to the formation of HT-induced pollen abortion by disrupting the sugar utilization in HT-stressed anther. HT exposure suppressed the activities of cell wall and vacuolar invertase, hexokinase, and ADP-glucose pyrophosphorylase in developing anther, while it was opposite for the effect of HT exposure on sucrose synthase and fructokinase. HT-induced suppression of OsCWIN3 in the anther walls might be strongly responsible for the HT-induced impairments of sugar utilization in HT-stressed anthers.

ABA-triggered ROS burst in rice developing anthers is critical for tapetal programmed cell death induction and heat stress-induced pollen abortion.

High temperatures (HT) cause pollen abortion and poor floret fertility in rice, which is closely associated with excessive accumulation of reactive oxygen species (ROS) in the developing anthers. However, the relationships between accumulation of abscisic acid (ABA) and ROS, and their effects on tapetum-specific programmed cell death (PCD) in HT-stressed anthers are poorly characterised. Here, we determined the spatiotemporal changes in ABA and ROS levels, and their relationships with tapetal PCD under HT exposure. Mutants lacking ABA-activated protein kinase 2 (SAPK2) functions and exogenous ABA treatments were used to explore the effects of ABA signalling on the induction of PCD and ROS accumulation during pollen development. HT-induced pollen abortion was tightly associated with ABA accumulation and oxidative stress. The higher ABA level in HT-stressed anthers resulted in the earlier initiation of PCD induction and subsequently abnormal tapetum degeneration by activating ROS accumulation in developing anthers. Interactions between SAPK2 and DEAD-box ATP-dependent RNA helicase elF4A-1 (RH4) were required for ABA-induced ROS generation in developing anthers. The OsSAPK2 knockout mutants showed the impaired PCD responses in the absence of HT. However, the deficiency of SAPK2 functions did not suppress the ABA-mediated ROS generation in HT-stressed anthers.