The quest for molecular markers indicating root growth in microbially treated tomato (Solanum lycopersicum) plants

Abstract

Roots are essential plant organs for anchorage in soil, uptake of water with nutrients, storage of photosynthates, and microbial interactions. More knowledge on microorganisms stimulating root growth is needed to control root development of cultured plants. A marker-assisted approach would facilitate vast screenings of microbes for eventual effects on root development. It was aimed to select for transcripts that report on root growth stimulation at the early tomato plant growth stage upon microbial treatments. Microbially treated tomato (Solanum lycopersicum) plants were cultivated in stone wool slabs and screened for genes that increased or decreased in differential expression upon increased root growth, by RNAseq. Expression of 21 selected genes was measured by quantitative polymerase chain reaction (qPCR) in relation with stimulated root growth, recorded by X-ray microtomography, of microbially treated tomato plants cultivated in stone wool blocks. Two genes were identified of which expression significantly correlated with high measured root length, and for one also with high measured shoot wet and dry weight. The translated products, both involved in modulation of Rubisco activity, were a chloroplast-localized acetyltransferase (SlSNAT2) and a Rubisco activase (Rca). Transcripts whose translated products modulate Rubisco activity can serve as candidates for reporting on early root development upon microbial inoculation.

Keywords: Verrucomicrobium; RNAseq; X-ray microtomography; microbial inoculant; root development; root growth indicator; stone wool; tomato plants.

Figure 1.

Box plot (maximum, 3rd, 2nd, and 1st quartiles, minimum values) of root length measured over time in stone wool slabs (A), and number of adventitious roots after 21 d (B). Roots of tomato plants grown in stone wool slabs (n = 10) were measured at 7, 10, 14, and 21 d after sowing. Box plot with * indicate significant different average value from control, as determined by Students t-test.

Figure 2.

Box plot (maximum, 3rd, 2nd, and 1st quartiles, minimum values) of shoot fresh weight (A) and length values (B) and number of compound leaves (C) of tomato plants (n = 10) grown in stone wool slabs and sampled after 21 days. Box plot with * indicate significant different average value from control, as determined by Students t-test.

Figure 3.

Principle component analysis biplot (A), demonstrating differences between gene expression profiles of tomato plants under 16 microbial and control treatments, and CCA biplot (B), demonstrating the relationship between gene expression profiles and shoot (CL, SL, SW) and root (AR, RL) parameters: CL, number of compound leaves; SL, shoot length; SW, shoot fresh weight; AR, number of adventitious roots; and RL, root length.

Figure 4.

Box plot (maximum, 3rd, 2nd, and 1st quartiles, minimum values) of root length (A), shoot dry (B), and shoot fresh weight (C) values of tomato plants grown in stone wool blocks (n = 5) measured after 17 d under five different microbial and control treatments. Root length was determined by X-ray microtomography. Box plot with * indicate significant different average value from control, as determined by Student t-test.