Researchers have identified novel factors involved in controlling the angles at which leaves emerge, possibly improving crop productivity.
Rice is a staple food in Asia and some parts of the Pacific. It should then come as no surprise that over 90 per cent of the world’s rice is produced and consumed in the Asia-Pacific region. Given that agricultural land is limited and the human population is rapidly growing, there is a need to find ways to improve food crop productivity to meet the increasing demand.
“Crop architecture”, or the design of the crop plant, can have a major influence on its produce. Hence, recognising crop architecture patterns and underlying biology could help improve agricultural productivity.
In a study by researchers from Shanghai Jiao Tong University and the Chinese Academy of Sciences, they found genetic factors that control leaf inclination in rice, Oryza sativa. Leaf inclination, or the angle at which the leaf emerges from the stem, determines its exposure to sunlight and in turn, its photosynthetic capacity. By identifying genetic variants with leaf angles that favour the ideal plant architecture, we could potentially breed rice varieties with higher productivity, improving crop yield.
It is known that some plant hormones, like auxin and brassinosteroids (BRs), control leaf inclination. Based on previous research, BR-deficient mutants displayed upright leaf architecture with decreased inclination while rice plants with decreased auxin levels exhibit increased leaf inclination. Auxin mutants with changed leaf angles have been shown to present altered BR responses. However, the mechanisms behind these effects remain to be known.
To get a better understanding of the auxin-BR crosstalk, the researchers first screened a rice T-DNA insertion population and identified an auxin insensitive mutant arr1, which was confirmed through genomic analysis. When treated with an auxin stimulant, the mutant plants showed significantly lower levels of auxin signalling factors compared to wild type plants, confirming the suppressed auxin response of arr1.
Then, they compared the leaf inclination and lamina joint (the region connecting the leaf blade and sheath/stalk) of wild type plants and arr1, and found that the arr1 mutant had enlarged leaf angles compared to the wild type. Furthermore, they observed that the cells closer to the stalk at the leaf joint of the mutant were twice as long as those of wild type plants, resulting in an enlarged inclination.
Through genetic analysis, the team found that the arr1 mutant displayed an increased expression of OslAA6 gene, which led to increased leaf inclination due to gain-of-function of the protein. OslAA6 is also thought to determine the leaf angle due to its significantly high expression pattern in the lamina joints.
By looking at the interacting partners of OslAA6, the researchers were able to pinpoint that OslAA6 controlled leaf inclination by suppressing the auxin response factor, OsARF1. In addition to that, the team also found that OsBZR1, an important transcription factor in the BR signalling pathway, binds to the promoter of OslAA6 and controls its expression, indicating the role of OslAA6 in the auxin-BR pathway crosstalk.
Altogether, these findings put forward that OslAA6 acts as a link between the auxin and BR signalling pathways in controlling leaf inclination, which could open new doors for the development of rice crop varieties with higher photosynthetic efficiency.
“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,” said Professor Hongwei Xue.
Source: Xing et al. (2022). Rice OsIAA6 interacts with OsARF1 and regulates leaf inclination.The Crop Journal.