It alludes to the importance of each gene in relation to PC1. If, for example, PC1 accounts for 70% variation in your dataset, then these genes are the main sources of that variation. Sign / directionality is important: for example, it implies that MALAT1 will be higher in certain samples whose loading values are negative along PC1, whereas the reverse is true for all other genes in this plot that you are showing.
It is essentially plotting the same as that produced by my own function,
plotLoadings(), from PCAtools: Determine the variables that drive variation among each PC