## 2 Results  
Increased Plant Growth and Higher Plant Biomass at 21 Days Post-Inoculation with Bacteria PsJN in a \"Closed-Plate\" System  
Our pilot experiment utilizing the traditional closed-plate system showed that PsJN promote the growth and heat tolerance to Arabidopsis plants. For the control plants, a high temperature resulted in a decrease in the total root length, with this reduction ranging from 21% (at 2 DAI) to 76% (at 21 DAI) (Figure S1a). When the total root length was discriminated into the primary and branched root components, we found a similar decline in the root lengths due to the high temperature. The primary root lengths showed a reduction that was between 21% and 48%, while the branched roots showed a larger amount of reduction that was between 52% and 77% from 2 to 21 DAI, indicating the strong effect of a high temperature on the latter root types (Figure S1b,c). Although the increased temperature detrimentally affected the root lengths, this was ameliorated by the inoculation of them with PsJN, the magnitude of which varied in the root types. At 21 DAI and at a high temperature, the PsJN-inoculated plants showed a 123% increase in total root lengths when they were compared to the control plants (Figure S1a). Interestingly, although this positive bacterial inoculation effect on the primary root was strong at the start of the experiment (at 52%), this declined towards the end of the growing period. The branched roots also showed the same decreasing inoculation effect, which was from 225% to 136% (Figure S1b,c). Under the ambient temperature at 21 DAI, the bacterial inoculation increased the total root lengths by 37% from that of the control plants, and this was mainly observed in the branched roots. However, this positive effect of bacterial inoculation on the total root lengths under the ambient temperature, was 3.3 times lower than when it was compared to its effect under the high temperature (Figure S1a). The root and shoot weights were reduced by the high temperature and the ambient temperature (at 50% and 20% reduction rates, respectively) (Figure S1d,e). The bacterial inoculation minimized this reduction under the high temperature by increasing the root weights by 6% and the shoot weights by 5% when they were compared to the control plants. However, a stronger effect of bacterial inoculation was observed under the ambient temperature, with an increase of 42% and 16% for the root and shoot weights, respectively (Figure S1d,e). The conventional \"closed-plate\" system, which was coupled with the WinRhizo imaging platform, allowed the plant-bacteria co-cultivation and periodic imaging and trait analysis to be performed (Figure S1). However, this system did not allow the natural growth of the shoots and roots, but instead, it enclosed the whole plant inside the plate, providing restrictions on the plant's development. In addition, the software analysis tool was not sensitive enough to accurately discriminate between the higher order root types (1 st- and 2 nd-order lateral), particularly at the later stages of the roots' growth. Moreover, it did not enable us to save the previously analyzed root structures for them to be appended for the succeeding growth stage analysis, which provides a more efficient and accurate way of monitoring the root morphologic growth. In-Depth Root Characterization Shows PsJN-Imparted Growth Promotion on Root System Architecture (RSA) as Influenced by Temperature and Time  
The GrowScreen-Agar II platform addressed all of the issues of the traditional \"closed plate\" approach. First, the customized plates for the imaging system allowed the unobstructed growth of the rosette and the inflorescence (Figure 1a) due to there being open holes. The plates were custom-made for the imaging system for the plants to be consistently positioning which is critical for the consequential imaging and image superimposition during the analysis stage. The infrared light that was used for the root imaging prevented the disturbance or damage occurring to the root tissues.