Loss of Arabidopsis matrix metalloproteinase‐5 affects root development and root bacterial communities during drought stress

Matrix metalloproteinases (MMPs) are zinc‐dependent endo‐peptidases that in mammals are known to be involved in remodeling the extracellular matrix (ECM) in developmental and pathological processes. In this study, we report At5‐MMP of Arabidopsis thaliana to be important for root development and root bacterial communities. At5‐MMP is mainly localized in the root vasculature and lateral root, an At5‐MMP T‐DNA insertion mutant (mmp5 KO) showed reduced root growth and a lower number of root apexes, causing reduced water uptake from the soil. Subsequently, mmp5 KO is sensitive to drought stress. Inhibited auxin transport was accompanied with resistance to indole‐3‐acetic acid (IAA), 2, 4‐dichlorophenoxyacetic acid (2, 4‐D), and 1‐naphthaleneacetic acid (NAA). The content of endogenous abscisic acid (ABA) was lower in roots of mmp5 KO than in wild type. Genes responsive to ABA as well as genes encoding enzymes of the proline biosynthesis were expressed to a lower extent in mmp5 KO than in wild type. Moreover, drought stress modulated root‐associated bacterial communities of mmp5 KO: the number of Actinobacteria increased. Therefore, At5‐MMP modulates auxin/ABA signaling rendering the plant sensitive to drought stress and recruiting differential root bacterial communities.