MOSFET in place of potentiometer
My comment about using a MOSFET as a variable resistor was a general suggestion (before the presence of the schematic), now it became nearly meaningless after seeing the schematic.
It appears that your aim is to adjust the output voltage via the Arduino. Then you have these options:

As the schematic is a Boost Converter, you can simply remove the IC, place the MOSFET in place of the IC and drive it with PWM coming from Arduino. You can use the analog inputs to measure the output and to modify the PWM duty-cycle and adjust the output voltage: Measure the output through the divider -&gt; adjust the PWM duty-cycle -&gt; measure the output again -&gt; adjust the duty cycle again -&gt; ...




simulate this circuit &ndash; Schematic created using CircuitLab
Fig: Principle schematic of an Arduino-controlled Boost Converter.

As already stated by others, you can use a digital potentiometer (make sure the voltage across the digi-pot does not exceed the abs max voltage).

You can use a DAC to directly adjust the output. Here is a tutorial of mine. Note that there's no need to use a DAC IC. Instead, you can build a crude DAC with PWM + RC Filter + Opamp Buffer.