Original Post: ICRISAT Happenings

New study reveals how in some lines male sterility can be reversed to produce hybrids faster and cheaper

Researchers have identified how temperature controls male fertility in some lines of pigeonpea and have unraveled the phenomenon’s molecular mechanism in a recently published study in The Plant Genome. They have also shown that sterility can be reversed with auxin treatment. The new findings are expected to pave way for techniques that can reduce the cost and effort in hybridizing the crop, and lead to increased yields. Pigeonpea is extensively grown and consumed in South Asia and Eastern Africa, being one of the oldest food crops and a staple source of protein.

Sterility transition in pigeonpea

Through their research, the authors demonstrated that pigeonpea lines turning fertile in response to the environment, called Environment Sensitive Genic Sterile (EGMS) lines, can go from being male sterile to male fertile if the temperature of the growing environment is reduced to 24 degree Celsius.

“Male sterile condition can be reversed by reducing the day temperature below the critical threshold temperature of 24 degree Celsius during the tetrad and microspore stage of pollen development,” said Lekha Pazhamala, the study’s first author and Systems Biology scientist at ICRISAT.

After determining the threshold temperature, the team set out to work backwards from protein expression to the metabolic pathway and then onto the gene expression to understand the molecular basis of sterility transition. They zeroed in on a key protein – a transcription factor. Transcription factors are known to play an important role in DNA transcription in the larger process of protein synthesis.

“The transcription factor called REVEILLE 1 regulates auxin levels, which explains fertility transition in response to day temperature, especially morning hours,” Dr Rajeev Varshney, the study’s lead, said while adding that the research is a result of what scientists today call Systems Biology – a combinatorial approach of transcriptomics, proteomics, metabolomics and computational genomics. Dr Varshney is Director for the Genetic Gains Research Program at ICRISAT.

Auxins are hormones plants produce for growth. By determining the temperature-auxin-transcription factor-pollen stage link, researchers were able to show that external auxin treatment can satisfactorily reverse sterility even when the day temperature is higher than the threshold.

Dr Rachit Saxena, a co-lead of the study and Senior Scientist in Applied Genomics at ICRISAT, explains, “Reversal of male sterility through external application of a common naturally occurring auxin, Indole-3-acetic acid, confirmed what the study found – that disturbed auxin levels causes thickening of pollen wall and inhibit nutrient uptake by developing pollen, leading to their starvation and sterility.”

Study background and significance

More than a decade ago, ICRISAT’s pigeonpea breeders observed sterility transition in some pigeonpea lines. But, until the present study, it was not clear how the transition happened and more importantly, how it can be regulated. In the intervening years, ICRISAT and partnering institutions
developed the world’s first pigeonpea hybridization technique that uses three lines to produce a hybrid. The hybrids from the three-line system posted 40% more yields than pure varieties.

However, producing a hybrid using the three-line system can be cumbersome. If a two-line system can be developed for pigeonpea with EGMS lines, as was done for rice, it can significantly reduce the cost and effort of hybrid production. Thus, began an effort to study the EGMS pigeonpea lines at ICRISAT, culminating in the present study.

“With an EGMS line, precise temperature control can be used for both production of hybrid seeds for farmers and to multiply the hybrid itself,” said the study’s co-lead, Prof Wolfram Weckwerth, Director, Vienna Metabolomics Center at University of Vienna. “And in environments where day temperatures do not favorably fluctuate, auxins can be used to achieve sterility to fertility transition. We look forward to see the study’s results reach farmers’ fields.”

The findings of the study ‘Multiomics approach unravels fertility transition in a pigeonpea line for a two‐line hybrid system’ can be found here.This work contributes to UN Sustainable Development Goal.