Decoding Leaf Angle Genetics: Larger Slant for a Better Crop Yields

Plants have long been our primary source of nutrition. The demand for food products is constantly increasing as the human population grows at a rapid rate. Because agricultural land is limited, meeting this rising demand will necessitate finding new ways to increase the productivity of existing crops.

Crop architecture, or the design of the crop plant, has a significant impact on its yield. Identifying crop architecture patterns and the biology that underpins them could thus aid in increasing agricultural productivity.

A group of Chinese researchers has now delved deeper into the genetic basis of crop architecture using rice as a model plant system in a new study published in The Crop Journal.

Findings of Study:

Photosynthesis, the process by which plants convert light energy into chemical energy in the form of food, takes place primarily on leaves. Furthermore, the angle at which the leaf emerges from the stem, or "leaf inclination," determines its exposure to sunlight and, as a result, its photosynthetic capacity. The researchers discovered genetic factors that control leaf inclination in rice (Oryza sativa) in their study.

Professor Hongwei Xue, the study's lead author, elaborates on the implications of their findings: "The leaf inclination is a key factor in determining the shape of the rice leaf's light-receiving part. Identifying genetic variants with a leaf angle that favours ideal plant architecture can aid in the development of higher-yielding rice varieties."

Several plant hormones are known to control leaf inclination, including "auxin" and "brassinosteroids" (BRs). Interestingly, mutants lacking in BRs have erect leaf architecture and lower inclination, whereas rice plants with lower auxin levels have higher leaf inclination. Auxin mutants with different leaf angles have been shown to have different BR responses. The exact mechanisms governing these effects, however, are unknown.

The researchers began by screening a rice T-DNA insertion population for auxin insensitive mutant arr1 in order to better understand the auxin-BR cross-talk. Genomic analysis was used to confirm the mutation. When the mutant plants were given an auxin stimulant, they had significantly lower levels of auxin signalling factors like OsIAA1, OsIAA9, OsIAA19, and OsIAA24 than wild-type plants.

The leaf inclination and lamina joint (region connecting the leaf blade and sheath/stalk) of wild type and arr1 plants were then compared. In comparison to the wild type, the arr1 mutant had larger leaf angles. In addition, the mutant's adaxial cells (cells closer 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 increased leaf inclination due to the gain-of-function of the protein, according to genetic analysis. OsIAA6's expression pattern in the lamina joints was also found to be very high, implying that it plays a role in determining the leaf angle.

When the researchers looked into OsIAA6's interacting partners, they discovered that it controlled leaf inclination by suppressing the auxin response factor OsARF1.

Furthermore, they discovered that OsBZR1, a key transcription factor in the BR signalling pathway, binds to the OsIAA6 promoter and regulates its expression, implying that OsIAA6 plays a role in the auxin-BR pathway crosstalk.

These findings suggest that OsIAA6 mediates leaf inclination by acting as a link between the auxin and BR signalling pathways, an insight that could lead to new rice crop varieties with higher photosynthetic efficiency. It is unquestionably a step forward in increasing rice production, which is the staple food for the vast majority of humanity.

(Source: Phys.org)