There is a built-in function for that.
Here is sample code:
regions_to_be_marked = randn(40,1); % array of the points you want to plot vertical line (x axis values)
x_data = randn(100,1); % x data to plot
y_data = randn(100,1); % y data to plot
hFig = figure; % figure handle
hAxes = axes(hFig); % axis handle
hPlot = plot(hAxes,x_data,y_data,'LineStyle','none','Marker','*'); % your actual plot
hold on; % holds current plot
% plot each region in for loop
for i = 1:numel(regions_to_be_marked)
xline(hAxes, regions_to_be_marked(i),'LineWidth',2,'Color','red');
end
