## 2 Results
The depth of the system was increased by almost 100% from the closed plates to a maximal 20 cm depth. As a result, the Arabidopsis plants grew well, simulating the unobstructed upward growth of the shoots that were exposed to light and air, and the undisturbed downward growth of the roots that were in the dark. The dark environment ensured that no skewing occurred during the gravitropic growth process (Figure 1b). Second, with the associated image analysis software, the Colour segmentation tool (shoot) and GrowScreen-Root (root), several traits were quantitively measured; in particular for the roots, which is normally a challenge in a time-course study (Figure 1c). The GrowScreen-Agar II platform also provided an opportunity to study the growth of the roots. The GrowScreen-Agar II platform was designed to study the growth of the roots. nity to further investigate the architecture of the root system by separating the branched roots into 1 st- and 2 nd-order lateral roots and by measuring other quantifiable spatial and temporal parameters, thereby highlighting the effects of bacteria under two different temperatures. The platform is suitable for plant-microbe interaction studies, as we could confirm that PsJN which was inoculated at the germinated seed stage was also found in the root-tip regions of the 21-day-old plants (Figure S2), while at the same time, the plates looked clean and did not show any signs of colony growth on the agar (Figure S3). The high temperature decreased the total root lengths by 63% from that of the ambient temperature condition, although with them being inoculated, the decrease of this was smaller at 43% (Figure 2a). The PsJN application increased the total root lengths of the plants under both the ambient and high-temperature conditions, and this was shown to occur consistently from 5 DAI up to 21 DAI (Figure 2a). The difference between the inoculated and control plants peaked at 12 DAI by 103% for the ambient temperature and 202% for the high temperature, before slowly dropping after this. At the end of the growing period, under the high temperature, the bacterial inoculation increased the total root lengths by 52% from that of the control plants. This was two times more than the increase that was observed under the ambient temperature (Figure 2a, Table S1). The total root growth rates also indicated the same trend, with the high temperature causing a 51% reduction from that of the ambient temperature condition (Figure 2f). Under the high temperature, the  
Figure 1: **GrowScreen-Agar II: Plant cultivation setup and root/shoot image acquisition and analysis. ****(a)** Arabidopsis plants growing in customized plates and magazine (product specification on Figures S1 and S2, respectively). Black plate collars provide the background for the growing shoots outside of the plates, while at the same time they exclude light entering the top of the metal magazine (**bottom** panel) to provide dark environment for the roots. (**b)** Overview of a single plate that is manually transferred to an imaging system (Figure S3) equipped with cameras for imaging the shoots and the roots, generating two images: top view of the shoot(s) and the whole root system. (**c)** (**Top**) Analysed image of a rosette using the Colour segmentation tool that computes the sum of white pixels as a proxy to compute the projected leaf area [59]. (**Bottom**) Analysed image of a root system using the GrowScreen-Root software [52]. Different root types are distinguished by color: green for primary roots, red for 1 st-order lateral roots, and blue for 2 nd-order lateral roots. The whole image area can also be divided horizontally into several sections to extract root length density per layer. inoculated plants performed better than the control plants did, with there being an increase of between 178% and 227% from 5 to 9 DAI. On the other hand, this effect was lower, and it was between 92% and 121% under the ambient temperature.