The rice miR171b–SCL6-IIs module controls blast resistance, grain yield, and flowering

MicroRNAs (miRNAs) act as regulators of plant development and multiple stress responses. Here we demonstrate that the rice miR171b-SCL6-IIs module regulates the balance between blast resistance, grain yield, and flowering. miR171b-overexpressing rice plants (OX171b) displayed increased rice blast resistance accompanied with enhanced defense responses and late heading, whereas blocking miR171b expression in rice (MIM171) led to greater susceptibility to blast disease, associated with compromised defense responses and early heading. Either overexpressing or silencing of miR171b significantly affected plant height and number of filled seeds per panicle (seed-setting rate), resulting in decreased grain yield. miR171b targets SCL6-IIa, SCL6-IIb, and SCL6-IIc, whose expression was suppressed in OX171b but increased in MIM171. Mutants of SCL6-IIa, SCL6-IIb, and SCL6-IIc all displayed phenotypes like that of OX171b, including markedly increased blast disease resistance, slightly decreased grain yield, and delayed flowering. Amounts of miR171b increased gradually in leaves during the vegetative stage but decreased gradually in panicles during the reproductive stage, whereas SCL6-IIs displayed the reverse expression pattern. Together, these results suggest that the expression of miR171b was time- and space-dependent during the rice growth period and regulated the balance between rice blast disease resistance, grain yield, and flowering via SCL6-IIs, and that appropriate accumulation of miR171b is essential for rice development.