BACKGROUND: The production and use of biologically derived soil additives is one of the fastest growing sectors of the fertilizer industry. These products have been shown to improve crop yields while at the same time reducing fertilizer inputs to and nutrient loss from cropland. The mechanisms driving the changes in primary productivity and soil processes are poorly understood and little is known about changes in secondary productivity associated with the use of microbial products. Here we investigate secondary metabolic responses to a biologically derived soil additive by monitoring changes in the phenlypropanoid (PP) pathway in Arabidopsis thaliana.

RESULTS: This study was designed to test the influence of one of these products (Soil Builder™-AF, SB) on secondary metabolism after being applied at different times. One time (TI) application of SB to Arabidopsis increased the accumulation of flavonoids compared to multiple (TII) applications of the same products. Fourteen phenolic compounds including flavonols and anothocyanins were identified by mass spectrometry. Kaempferol-3,7-O-bis-α-L-rhamnoside and quercetin 3,7-dirhamnoside, the major compounds, increased 3-fold and 4-fold, respectively compared to control in the TI treatment. The most abundant anthocyanin was cyanidin 3-rhamnoglucoside, which increased 3-fold and 2-fold in TI compared to the control and TII, respectively. Simultaneously, the expression of genes coding for key enzymes in the PP pathway (phenylalanine ammonia lyase, cinnamate 4-hydroxylase, chalcone synthase, flavonoid-3'-O-hydroxylase, flavonol synthase1 and dihydroflavonol-4-reductase) and regulatory genes (production of anthocyanin pigment2, MYB12, MYB113, MYB114, EGL3, and TT8) were up-regulated in both treatments (TI and TII). Furthermore, application of TI and TII induced expression of the lignin pathway genes (hydroxyl cinamyl transferase, caffeyl-CoA O-methyl transferase, cinnamyl alcohol dehydrogenase, cinnamyl-CoA reductase, secondary wall-associated NAC domain protein1, MYB58 and MYB63 resulting in higher accumulation of lignin content compared to the control.

CONCLUSIONS: These results indicate that the additions of microbially based soil additives have a perceptible influence on phenylpropanoid pathway gene regulation and its production of secondary metabolites. These findings open an avenue of research to investigate the mode of action of microbially-based soil additives which may assist in the sustainable production of food, feed, fuel and fiber.

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Notes/Citation Information

Published in BMC Plant Biology, v. 14, no. 84, p. 1-14.

© 2014 Ali and McNear; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.

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1471-2229-14-84-s1.doc (153 kB)
The flavonoid biosynthesis pathway that leads to the production of anthocyanidins and flavonols in Arabidopsis; several transcription factors (MYB, bHLH and WD-40) are indicated along the branches that are likely involved in the transcriptional regulation of the structural genes.

1471-2229-14-84-s2.pdf (157 kB)
Relative transcript abundance of acetyltranseferase genes (At1g03495, At1g03940, and At3g29590 ) known to be involved in the acylation (A) UDP-glucosyltransferase (At4g14090 and At5g17030 ) and GSTs (At1g02920) genes known to be involved in the glycosylation (B), and rhamnose synthesis genes (RHM1, RHM2 and RHM3) involved in the rhamnosylation (C) of flavonoids treated once (TI) and multiple times (TII) with SB in Arabidopsis thaliana.

1471-2229-14-84-s3.pdf (156 kB)
Relative transcript abundance of cinnamyl alcohol dehydrogenase family genes (CAD1, CAD3, CAD4, CAD5, CAD7 and CAD8) known to be involved in lignin biosynthesis treated once (TI) and multiple times (TII) with SB in Arabidopsis thaliana.

1471-2229-14-84-s4.pdf (157 kB)
Relative transcript abundance of laccase (LAC4 and LAC17) genes known to be involved in lignin biosynthesis (A) and transcription factors (SND1, MYB58 and MYB63) (B) are known to regulate lignin biosynthesis in Arabidopsis treated once (TI) and multiple times (TII) with SB in Arabidopsis thaliana.

1471-2229-14-84-s5.doc (35 kB)
Basic chemical properties of Soil Builder used in the present study.

1471-2229-14-84-s6.doc (79 kB)
Primers used for qRT-PCR analysis and expected size for the amplified fragments.