Abstract
Improving grain yield in the staple food crop rice has been long sought goal of plant biotechnology. One of the traits with significant impact on rice breeding programs is peduncle elongation at the time of heading failing which leads to significant reduction in grain yield due to incomplete panicle exsertion. To decipher transcriptional dynamics and molecular players underlying peduncle elongation, we performed RNA sequencing analysis of elongating and non-elongating peduncles in two Indian cultivars, Swarna and Pokkali, at the time of heading. Along with genes associated with cell division and cell wall biosynthesis, we observed significant enrichment of genes associated with auxins, gibberellins, and brassinosteroid biosynthesis/signaling in the elongating peduncles before heading in both the genotypes. Similarly, genes associated with carbohydrate metabolism and mobilization, abiotic stress response along with cytokinin, abscisic acid, jasmonic acid, and ethylene biosynthesis/signaling were enriched in non-elongating peduncles post heading. Significant enrichment of genes belonging to key transcription factor families highlights their specialized roles in peduncle elongation and grain filling before and after heading, respectively. A comparison with anther/pollen development-related genes provided 76 candidates with overlapping roles in anther/pollen development and peduncle elongation. Some of these are important for carbohydrate remobilization to the developing grains. These can be engineered to combat with incomplete panicle exsertion in male sterile lines and manipulate carbohydrate dynamics in grasses. Overall, this study provides baseline information about potential target genes for engineering peduncle elongation with implications on plant height, biomass composition and grain yields in rice.
Highlights
With huge diversity in morphological architectures of flowering plants, a thorough understanding of plant morphology is essential to appreciate the diverse shapes and forms exhibited by the plant world and vital to engineering crop plants with improved agricultural traits
Lack of a comprehensive study to understand the overall gene expression dynamics during panicle elongation at the time heading is still limiting our understanding of panicle exsertion process in rice. To fill this gap in our understanding, we investigated the transcriptional dynamics during peduncle elongation at the time of heading in two indica genotypes of rice, Swarna and Pokkali, so that genotype-specific effects could be minimized
Carbohydrate Metabolism and Transport Since the peduncle comprises an essential component of the transport system facilitating carbohydrate mobilization during grain filling post heading, we investigated the expression of rice genes implicated in sucrose and starch metabolism as well as transport in our data (Supplementary Table 3C)
Summary
With huge diversity in morphological architectures of flowering plants, a thorough understanding of plant morphology is essential to appreciate the diverse shapes and forms exhibited by the plant world and vital to engineering crop plants with improved agricultural traits. A slight modification in plant architecture can have a profound effect on the agronomic performance of crop plants. This was clearly demonstrated during the green revolution, where breeding for semi-dwarf. Elongation of peduncle at the time of heading facilitates the emergence of panicle from the flag leaf sheath, commonly known as panicle exsertion, which is crucial for anther dehiscence and pollination (Bardenas, 1965). Extremes of temperature and drought stress at the time of heading, result in dramatic yield losses by inhibiting peduncle elongation and, subsequent panicle exsertion and anther dehiscence in rice (Muthurajan et al, 2011; He and Serraj, 2012; Wu et al, 2016). One of the common strategies used to combat this challenge involve spray of gibberellins but it significantly enhances the cost of production (Yin et al, 2007)
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