Abstract
Canopy architecture is critical in determining the light interception and distribution, and subsequently the photosynthetic efficiency and productivity. However, the physiological responses and molecular mechanisms by which pear canopy architectural traits impact on photosynthesis remain poorly understood. Here, physiological investigations coupled with comparative transcriptomic analyses were performed in pear leaves under distinct training systems. Compared with traditional freestanding system, flat-type trellis system (DP) showed higher net photosynthetic rate (PN) levels at the most time points throughout the entire monitored period, especially for the interior of the canopy in sunny side. Gene ontology analysis revealed that photosynthesis, carbohydrate derivative catabolic process and fatty acid metabolic process were over-represented in leaves of DP system with open-canopy characteristics. Weighted gene co-expression network analysis uncovered a significant network module positive correlated with PN value. The hub genes (PpFKF1 and PpPRR5) of the module were enriched in circadian rhythm pathway, suggesting a functional role for circadian clock genes in mediating photosynthetic performance under distinct training systems. These results draw a link between pear photosynthetic response and specific canopy architectural traits, and highlight light harvesting and circadian clock network as potential targets for the input signals from the fluctuating light availability under distinct training systems.
Highlights
Canopy architecture is critical in determining the light interception and distribution, and subsequently the photosynthetic efficiency and productivity
The rates of photosynthetic rate (PN) were markedly higher in sun leaves than in shade leaves (Fig. 1B), which is probably due to higher light intensity in sunny side
Information about the mechanism of impact of training systems on photosynthesis is limited. Both Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that the up-regulated genes in DP training system participate in photosynthesis processes such as light harvesting (Fig. 4, Supplementary Table S3 and Table S4)
Summary
Canopy architecture is critical in determining the light interception and distribution, and subsequently the photosynthetic efficiency and productivity. In the field of fruit tree cultivation and management, training systems generally determine tree architecture, which represent spatial strategy for light interception and distribution within the canopy, and influence photosynthetic efficiency and productivity[7,8,9]. It is useful to understand how such architectural traits affect photosynthesis in order to fully to comprehend this complicated physiological process, which will be helpful for improving fruit quality through the correct choice of cultural practices. Traditional freestanding systems, such as spindle and delayed-open central leader, are widely employed in economic deciduous fruit tree pear. Better understanding of the effect of training systems on photosynthesis at the physiological and molecular level could provide basic information and important guidance for orchard management, and realize the promised increased in profitability in orchard
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