Rice Glucose 6-Phosphate/Phosphate Translocator 1 is required for tapetum function and pollen development

In plants, non-green plastids in heterotrophic tissues are sites for starch and fatty acids biosynthesis,which are essential for plant development and reproduction. Distinct from chloroplasts, the metabolites for these processes in non-green plastids have to be imported through specific transporters. Glucose 6-Phosphate/Phosphate Translocator 1 is required for the uptake of cytosolic Glucose 6-Phosphate into non-green plastids. In Arabidopsis, GPT1 has been demonstrated to play essential roles in male, female gametophyte and embryo development. However, the roles of GPTs in other species are yet largely unknown. Here, we reported that rice OsGPT1 is indispensable for normal tapetal degeneration and pollen exine formation during anther and pollen development. OsGPT1 is localized in the plastid and distributed in the anther wall layers and late-stage pollen grains. Different from the gametic defects caused by mutation in At GPT1, disruption of OsGPT1 does not affect male and female gamete transmission as well as embryo development. On the contrary, osgpt1 mutant exhibits delayed tapetum degeneration,decreased Ubisch bodies formation and thinner pollen exine, leading to pollen abortion at the mature stage. Furthermore, the expression of several genes involved in tapetal programmed cell death(PCD)and sporopollenin formation is decreased in osgpt1. Our study suggests that OsGPT1 coordinates the development of anther sporophytic tissues and the male gametophyte by integrating carbohydrate and fatty acid metabolism in the plastid.

OsMAPK6 Affects Male Fertility by Reducing Microspore Number and Delaying Tapetum Degradation in Oryza sativa L.

The mitogen-activated protein kinase(MAPK)cascade is important in stress signal transduction and plant development.In the present study,we identified a rice(Oryza sativa L.)mutant with reduced fertility,Oryza sativa mitogen-activated protein kinase 6(osmapk6),which harbored a mutated MAPK gene.Scanning and transmission electron microscopy,quantitative RT-PCR analysis,TUNEL assays,RNA in situ hybridization,longitudinal and transverse histological sectioning,and map-based cloning were performed to characterize the osmapk6 mutant.The gene OsMAPK6 was expressed throughout the plant but predominantly in the microspore mother cells,tapetal cells,and microspores in the anther sac.Compared with the wild type,the total number of microspores was reduced in the osmapk6 mutant.The formation of microspore mother cells was reduced in the osmapk6 anther sac at an early stage of anther development,which was the primary reason for the decrease in the total number of microspores.Programmed cell death of some tapetal cells was delayed in osmapk6 anthers and affected exine formation in neighboring microspores.These results suggest that OsMAPK6 plays pivotal roles in microspore mother cell formation and tapetal cell degradation.

ZmMS39 encodes a callose synthase essential for male fertility in maize(Zea mays L.)

Callose contributes to many biological processes of higher plants including pollen development,cell plate and vascular tissue formation,as well as regulating the transport function of plasmodesmata.The functions of callose synthase genes in maize have been little studied.We describe a maize male-sterile mutant 39(ms39)characterized by reduced plant height.In this study,we confirmed using CRISPR/Cas9 technology that a mutation in Zm00001d043909(ZmCals12),encoding a callose synthase,is responsible for the male sterility of the ms39 mutant.Compared with male-fertile plants,callose deposition around the dyads and tetrads in ms39 anthers was significantly reduced.Increased cell autophagy observed in ms39 anthers may have been due to the premature programmed cell death of tapetal cells,leading to collapse of the anther wall structure.Disordered glucose metabolism in ms39 may have intensified autophagy in anthers.Evaluation of the ms39 gene on maize heterosis by paired-crossed experiment with 11 maize inbred lines indicated that ms39 can be used for maize hybrid seed production.