Molecular Mechanism of Vegetative Growth Advantage in Allotriploid Populus

Abstract

Allotriploid poplar has a prominent vegetative growth advantage that impacts dramatically on lumber yield. The growth regulation is complex which involves abundant genes, metabolic and signaling pathways, while the information about the functional control process is very little. We used high-throughput sequencing and physiological index measurement to obtain a global overview of differences between allotriploid and diploid Populus. The genes related to plant growth advantage show a higher expression compared to diploid, and most of them are revolved around hormones, photosynthesis and product accumulation. Thus, allotriploid Populus showed more efficient photosynthesis, carbon fixation, sucrose and starch synthesis, and metabolism as well as augmented biosynthesis of auxin, cytokinin, and gibberellin. These data enable the connection of metabolic processes, signaling pathways, and specific gene activity, which will underpin the development of network models to elucidate the process of triploid Populus advantage growth.

Keywords: allotriploid; dosage effect; regulatory mechanism; vegetative growth advantage.

Figure 1

Transcription profile of differentially expresssed genes (DEGs) and real-time polymerase chain reaction (RT-PCR) validation. (A) The numbers and proportions of upregulated and downregulated genes in the 5th, 10th, and 25th leaves of triploid-F and triploid-S plants; (B) RT-PCR verification of randomly selected DEGs in the 5th, 10th, and 25th leaves of triploid-F and triploid-S plants.

Figure 2

Chlorophyll synthesis and degradation in triploid-F, triploid-S and diploid plants. (A) Differentially expressed genes (DEGs) involved in chlorophyll synthesis and metabolism at different leaf canopy positions when triploid-F and triploid-S plants were compared to diploid plants; (B) The number of chloroplasts, chlorophyll content and chlorophyllase activity in triploid-F, triploid-S and diploid plants, different lowercase letters represent significant differences at p < 0.05; (C) Chloroplast ultrastructure in the 5th, 10th and 25th leaves in allotriploid and diploid plants. Bar = 10 μm.

Figure 3

Photosynthesis in in triploid-F, triploid-S and diploid plants. (A) Differentially expressed genes (DEGs) involved in light reaction and carbon fixation on different leaf canopy positions when triploid-F and triploid-S plants were compared to diploid plants; (B) Net rates of photosynthesis on various leaf canopy positions in triploid-F, triploid-S plants and diploid plants.

Figure 4

Starch and sucrose synthesis and metabolism in triploid-F, triploid-S and diploid plants. (A) Differentially expressed genes (DEGs) associated with sucrose and starch synthesis and metabolism on different leaf canopy positions when triploid-F and triploid-S plants were compared to diploid plants; (B) Starch, sucrose, glucose and fructose content on different leaf canopy positions when triploid-F and triploid-S plants were compared to diploid plants; (C) SUS, SPS, and AMS enzyme activity on different leaf canopy positions when triploid-F and triploid-S plants were compared to diploid plants. Different lowercase letters represent significant differences at p < 0.05.

Figure 5

Hormone biosynthesis genes causing the upregulation of hormone in triploids. (A) Differentially expressed genes (DEGs) involved in plant hormone signal transduction on different leaf canopy positions when triploid-F and triploid-S plants were compared to diploid plants; (B) IAA, ZT, GA3 and ABA content in the 5th and 25th leaves of triploid-F and diploid plants. Different lowercase letters represent significant differences at p < 0.05.

Figure 6

DEGs involved in metabolism pathway in the leaves of triploid-F and triploid-S plants. Warm and cool colors represent upregulated and downregulated expression, respectively.

Figure 7

A model of the vegetative growth advantages of Populus allotriploid. Arrows and short-term indicate promotion and inhibition, respectively. The solid lines of mRNAs represent the dosage effect in Populus allotriploid, and the dashed lines of miRNAs represent no dosage effect in Populus allotriploid. 3-P: triphosphoglycerate; G₃P: triglyceride phosphate.