Genome Wide Analysis Of GmMAXs Genes Involved In Strigolactone Biosynthesis And Signaling And Characterization Of GmMAXs Genes

Strigolactones(SLs)represent an important new plant hormone class marked by their multifunctional role in plant and rhizosphere interactions.These compounds stimulate hyphal branching in Arbuscular mycorrhizal fungi(AMF)and seed germination of root parasitic plants.Legumes,such as Medicago truncatula,form mutualistic symbiotic relationships with nitrogen-fixing rhizobial bacteria.This occurs within specialized root organs(nodules)that provide the conditions required for nitrogen fixation.SLs play important roles in controlling root growth,shoot architecture,legume-symbionts interaction,and responses to phosphorous deficiency and various stresses.Despite recent extensive study in model plants,the components of SLs biosynthesis and signaling have not been unequivocally explored in soybean.Here,we identified the putative orthologs of the known SLs synthetic enzymes and signaling proteins in soybean genome.Soybean MORE AXILLARY BRANCHING(GmMAX)1,2,3,4,Gm(DWARF)GmD14,GmD53,GmD27,and GmPDR1 were identified with homology and tissue expression patterns in comparison to their orthologs coincident with SLs synthesis and signaling or in response to various abiotic stresses.Further we selected GmMAX1 a,GmMAX2a,GmMAX3 a,and GmMAX4 a and recombined into the pB7GW1WG2 RNAi destination vector via LR clonase to obtain the binary construct pB7GWIWG2(II)-RRp35S-GmMAX-RNAi.The functions of GmMAX1 a,GmMAX2a,GmMAX3 a,and GmMAX4 a were further characterized by generating knockdown chimerical plants.Transcript level of GmMAX1 a,GmMAX2a,GmMAX3 a,and GmMAX4 a was down-regulated in transgenic hairy root.GmMAX1 a,2a,3a,and 4a knockdown roots gave fewer nodules,whereas control hairy roots beard more nodules.The transcript level of most of the nodulation genes was also consistent with altered nodule numbers in knockdown chimerical plants.The GmMAX1 a,3a,and 4a-knockdown hairy root lines had reduced auxin,but increased jasmonate and abscisic acid levels while in GmMAX2a-knockdown hairy root line the IAA and JA increased significantly and ABA were not much altered compared to control.We further investigate the relationship of GmMAX2 a with auxin.The GmMAX2-KD hairy roots change the expression of YUCCAs and TAA1 s genes that ultimately increased the auxin level.Whereas YUCCAs generated soybean hairy roots up-regulated GmMAXs and GmD14,but reduced transcripts of SL repressor GmD53,suggesting that auxins are in cross-talk with SLs biosynthesis and signaling,so do ABA and JA hormones.This study provides new insights into the specific features of SLs biosynthesis and signaling in soybean nodulation and hormone signaling.