Abstract
Murashige & Skoog (MS) and Hoagland’s media were previously used for in vitro culture of Landoltia punctata. During subsequent ex vitro culture, the use of MS medium resulted in a higher growth rate, compared to Hoagland’s medium. Thus, a higher starch content of L. punctata in MS medium was previously hypothesized. Here, L. punctata strain 5632 was isolated and characterized using morphological characteristics and the atpF-atpH intergenic region. During early cultivation stage, fresh weight and relative growth rate in MS medium were lower than Hoagland’s medium. Conversely, starch content in MS medium was considerably higher than in Hoagland’s medium. Medium effects on expression of genes coding for starch-biosynthesis ADP-glucosepyrophosphorylase (AGPase) were determined. Genomic fragments of small (LeAPS) and large (LeAPL1) AGPase subunits were characterized. Differential expression between each AGPase subunit genes was observed in both media. Additionally, in MS medium, the highest correlation coefficients between starch content and gene expression was found with LeAPS (0.81) and followed by LeAPL3 (0.67), LeAPL2 (0.65) and LeAPL1 (0.28). In Hoagland’s medium, the coefficients of LeAPL3 (0.83) and LeAPL2 (0.62) were higher than LeAPS (0.18) and LeAPL1 (−0.62). This suggested different levels of contributions of these genes in starch biosynthesis in both media.
Highlights
Starch functions as an important energy reserve in plants[1]
The phylogenetic tree confirmed the presence of the paraphyletic subfamily Lemnoideae, consisting of Spirodela, Landoltia, and Lemna, and the monophyletic subfamily Wolffioideae, comprising of Wolffia and Wolffiella
The analysis indicated that amino acid positions 9, 192 and 257 of LeAPS (Fig. 4a) and 188 and 227 of LeAPL1 (Fig. 4b) of strain 5632 were more similar to the orthologs than strain 0202
Summary
Starch functions as an important energy reserve in plants[1]. During photosynthesis, carbon compounds are generated and converted into glucose that serves as the precursor for starch formation[1]. Expression of L. punctata AGPase subunit genes, including LeAPS, LeAPL1, LeAPL2 and LeAPL3, were affected by growth conditions[4,25]. A transcriptomic study showed that, when L. punctata was treated with uniconazole, expression of two AGPase large subunit genes and starch content were concurrently increased[25]. It was previously hypothesized that cultivation in MS medium resulted in higher starch accumulation that subsequently promoted ex vitro growth[26]. The cDNA fragments of LeAPS and LeAPL1, coding for AGPase large and small subunits, respectively, were cloned and compared with the reference sequences of L. punctata strain 02024. Genomic fragments of both genes were cloned, and their introns and exons were characterized. Correlation coefficients, between AGPase gene expression levels and starch content, were calculated to determine the contribution of each gene in starch biosynthesis, during the cultivation in MS and Hoagland’s media
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