Discovery reveals how two anther-specific genes coordinate pollen-wall formation and cellular balance, with potential applications in hybrid seed production.
Maize (Zea mays L.) researchers have identified two sugar transporters that play a central role in pollen development and male fertility, offering potential new genetic resources for hybrid seed production.
The study found that the anther-specific genes ZmSWEET6a and ZmSWEET6b perform two essential functions: supplying the materials needed to construct the pollen wall and maintaining the cellular balance that prevents premature tissue death.
The work was led by Professors Weiwei Jin and Wei Huang of China Agricultural University, in collaboration with researchers from Tianjin Agricultural University and the University of São Paulo in Brazil. The findings have been published online in The Crop Journal.
Male Sterility Supports Efficient Hybrid Production
Maize is China’s largest grain crop by both planted area and total production. It is also an important model for the use of heterosis, commonly known as hybrid vigour.
Producing reliable hybrid seed is critical to maintaining high and stable maize yields. Male-sterile lines, which do not produce viable pollen, can make that process considerably more efficient by reducing or eliminating the need for manual or mechanical detasselling.
Although numerous male-sterility genes have been cloned in maize, scientists still know relatively little about how genes involved in sugar metabolism influence male reproductive development, according to a press release.
Sugar Supply Proves Critical to Pollen-Wall Construction
The pollen wall protects pollen grains against environmental stresses. Its development begins when a carbohydrate-rich layer called the primexine forms on the surface of young microspores.
The new study shows that ZmSWEET6a and ZmSWEET6b become particularly important during the early stages of microspore development. Their expression peaks at stages S5 and S6, when they supply essential carbohydrate building blocks for primexine formation.
“We found that ZmSWEET6a/6b begin to play critical roles at early stages of microspore development, particularly during their peak expression window at stages S5–S6, when they supply essential polysaccharide precursors for primexine synthesis,” Huang says.
When both genes lose their function, pectin and xylan are not deposited properly. Without these polysaccharides, the primexine scaffold cannot assemble correctly and the pollen wall collapses.
Transporters Also Prevent Premature Cell Death
The researchers found that the two transporters do more than move sugars across cell membranes. They also help maintain the balance between sugar metabolism and reactive oxygen species, or ROS, within the anther.
In maize plants lacking functional ZmSWEET6a and ZmSWEET6b, ROS levels rose sharply at stage S6. In wild-type plants, comparable accumulation did not occur until stage S10.
This premature ROS burst triggered programmed cell death, or PCD, across all four layers of the anther wall. The resulting disruption of anther and pollen development caused complete male sterility.
“In addition to mediating transmembrane sugar transport, ZmSWEET6a/6b also maintain sugar–redox homeostasis in the anther, preventing premature ROS burst and ectopic initiation of PCD,” Huang says.
One Mechanism Links Metabolism and Fertility
Using cytological observations and multi-omics analyses, the team developed a model showing how sugar transport, ROS signalling and pollen-wall development are interconnected.
Loss of ZmSWEET6a/6b disrupts sugar homeostasis and sets off two linked processes: the primexine scaffold fails because essential polysaccharides are not deposited correctly, while the early ROS surge causes premature cell death in the anther wall.
The researchers therefore describe the two transporters as central coordinators of anther development. They simultaneously provide structural materials for the pollen wall and protect the anther’s redox balance.
“Deciphering the spatiotemporal coupling of carbohydrate metabolism and reproductive development is of great importance,” Jin says. “We hope this study offers new perspectives on the integration of metabolic and developmental pathways during plant reproduction.”
Findings Could Support Hybrid Maize Breeding
The discovery expands understanding of how carbohydrate allocation determines reproductive success in plants. It could also have practical implications for crop improvement.
By targeting ZmSWEET6a and ZmSWEET6b, breeders may be able to develop new male-sterile maize lines for more efficient hybrid seed production.
“These findings not only deepen our understanding of how carbohydrate allocation regulates reproductive success in plants but also provide valuable genetic resources for the development of novel male-sterile lines in hybrid crop breeding,” Jin says.
