Plants have long been the main source of nutrition. The demand for food production is always increasing as the human population grows exponentially. Since agricultural land is constrained, meeting this rising need will necessitate developing new ways to increase the productivity of existing crops.
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“Crop architecture”, or the design of the crop plant, has a significant impact on its yield. Recognizing crop architecture patterns and the biology that underpins them could thus aid in increasing agricultural production.
A group of Chinese researchers has looked deeper into the genetic foundation of crop design using rice as a model plant system in a new paper published in The Crop Journal.
Photosynthesis, the process by which plants transform light energy into chemical energy in the form of food, takes place mostly on leaves. Moreover, the angle at which the leaf arises from the stem, or “leaf inclination,” affects its sunlight exposure and, as a result, its photosynthetic potential.
The scientists determined genetic variables that affect leaf inclination in rice (Oryza sativa) in their investigation.
Adding to their understanding of the ramifications of their work, Professor Hongwei Xue, who led the study, clarifies, “The leaf inclination is an important trait determining the shape of the light-receiving part of the rice leaf. Identifying genetic variants with a leaf angle that favors ideal plant architecture can help in breeding rice varieties with higher productivity, improving the yield.”
Numerous plant hormones are known to control leaf inclination, including “auxin” and “brassinosteroids” (BRs). Surprisingly, mutants lacking in BRs have robust leaf architecture and lower inclination, but rice plants with lower auxin levels have higher leaf inclination.
Auxin mutants with different leaf angles have been demonstrated to have different BR responses. The exact processes driving these effects, however, are uncertain.
The scientists started by screening a rice T-DNA insertion population for auxin insensitive mutant arr1 to better understand the auxin-BR cross-talk. Genomic analysis was used to verify the mutation.
When the mutant plants were given an auxin stimulant, they had much lower levels of auxin signaling factors like OsIAA1, OsIAA9, OsIAA19, and OsIAA24 than wild-type plants.
The leaf inclination and lamina joint (area linking the leaf blade and sheath/stalk) of wild-type and arr1 plants were then compared. In comparison to the wild type, the arr1 mutant displayed larger leaf angles.
In addition, the mutant’s adaxial cells (cells closest to the stalk) at the leaf joint were twice as long as wild-type plants, resulting in a larger inclination.
The arr1 mutant had higher expression of the OsIAA6 gene, which resulted in enhanced leaf inclination due to the gain-of-function of the protein, according to genetic research. OsIAA6’s expression pattern in the lamina joints was likewise found to be very high, implying that it plays a function in modulating the leaf angle.
When the researchers looked into OsIAA6’s interaction partners, they discovered that it controlled leaf inclination by reducing the auxin response factor OsARF1. Furthermore, they discovered that OsBZR1, a major transcription factor in the BR signaling pathway, attaches to the OsIAA6 promoter and controls its expression, implying that OsIAA6 plays a role in the auxin-BR pathway crosstalk.
These results suggest that OsIAA6 mediates leaf inclination by acting as a connection between the auxin and BR signaling pathways, an understanding that could lead to novel rice crop variants with improved photosynthetic activity.
“Better plants can lead to a better life. The results in our study could contribute to a better understanding of plant growth and help design the ideal crops,” comments Professor Xue.
It is unquestionably a step forward in improving rice output, which is the basic diet for the vast majority of humanity.
Xing, M., et al. (2022) Rice OsIAA6 interacts with OsARF1 and regulates leaf inclination. The Crop Journal. doi.org/10.1016/j.cj.2022.02.010.