Genetic improvement of the shoot architecture and yield in soya bean plants via the manipulation of GmmiR156b.

The optimization of plant architecture in order to breed high-yielding soya bean cultivars is a goal of researchers. Tall plants bearing many long branches are desired, but only modest success in reaching these goals has been achieved. MicroRNA156 (miR156)-SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) gene modules play pivotal roles in controlling shoot architecture and other traits in crops like rice and wheat. However, the effects of miR156-SPL modules on soya bean architecture and yield, and the molecular mechanisms underlying these effects, remain largely unknown. In this study, we achieved substantial improvements in soya bean architecture and yield by overexpressing GmmiR156b. Transgenic plants produced significantly increased numbers of long branches, nodes and pods, and they exhibited an increased 100-seed weight, resulting in a 46%-63% increase in yield per plant. Intriguingly, GmmiR156b overexpression had no significant impact on plant height in a growth room or under field conditions; however, it increased stem thickness significantly. Our data indicate that GmmiR156b modulates these traits mainly via the direct cleavage of SPL transcripts. Moreover, we found that GmSPL9d is expressed in the shoot apical meristem and axillary meristems (AMs) of soya bean, and that GmSPL9d may regulate axillary bud formation and branching by physically interacting with the homeobox gene WUSCHEL (WUS), a central regulator of AM formation. Together, our results identify GmmiR156b as a promising target for the improvement of soya bean plant architecture and yields, and they reveal a new and conserved regulatory cascade involving miR156-SPL-WUS that will help researchers decipher the genetic basis of plant architecture.

GmmiR156b overexpression delays flowering time in soybean.

Soybean [Glycine max (L.) Merr.] is an important crop used for human consumption, animal feed and biodiesel fuel. Wering time and maturity significantly affect soybean grain yield. In Arabidopsis thaliana, miR156 has been proposed to regulate the transition from the juvenile to the adult phase of shoot development, which is accompanied by changes in vegetative morphology and an increase in reproductive potential. However, the molecular mechanisms underlying miR156 function in soybean flowering remain unknown. Here, we report that the overexpression of GmmiR156b delays flowering time in soybean. GmmiR156b may target SPL orthologs and negatively regulate GmSPLs, thereby delaying flowering in soybean under LD and natural conditions. GmmiR156b down-regulates several known flowering time regulators in soybean, such as GmAP1 (a, b, c), GmLFY2, GmLFY2, GmFULs, GmSOC1s, GmFT5a, and GmmiR172. These data show that a similar miR156-SPL regulatory module was conserved in the soybean flowering pathway. However, GmFULs, GmSOC1a and GmSOC1b were significantly suppressed under LD conditions but not under SD conditions, which is different in Arabidopsis that these genes were down-regulated irrespective of photoperiod. In addition, GmmiR156b was up-regulated by E1, E2 (GmGI), E3 and E4, which control flowering time and maturity in soybean, and suppressed E1 (E1-Like) and E2 (E2-Like) genes under LD conditions. These data indicated that the miR156-SPL regulatory module was also with some degree of divergent in soybean flowering pathway.