GmMAX2–D14 and –KAI interaction‐mediated SL and KAR signaling play essential roles in soybean root nodulation

Abstract

Summary Despite of important functions of strigolactones (SLs) and karrikins (KARs) in plant development, plant–parasite and plant–fungi interactions, their roles in soybean–rhizobia interaction remain elusive. SL/KAR signaling genes GmMAX2a, GmD14s, and GmKAIs are activated by rhizobia infection. GmMAX2a restored atmax2 root hair defects and soybean root hairs were changed in GmMAX2a overexpression (GmMAX2a‐OE) or knockdown (GmMAX2a‐KD) mutants. GmMAX2a‐KD gave fewer, whereas GmMAX2a‐OE produced more nodules than GUS hairy roots. Mutation of GmMAX2a in its KD or OE transgenic hairy roots affected the rhizobia infection‐induced increases in early nodulation gene expression. Both mutant hairy roots also displayed the altered auxin, jasmonate and abscisic acid levels, as further verified by transcriptomic analyses of their synthetic genes. Overexpression of an auxin synthetic gene GmYUC2a also affected SL and KAR signaling genes. GmMAX2a physically interacted with SL/KAR receptors GmD14s, GmKAIs, and GmD14Ls with different binding affinities, depending on variations in the critical amino acids, forming active D14/KAI‐SCFMAX2 complexes. The knockdown mutant roots of the nodule‐specifically expressing GmKAIs and GmD14Ls gave fewer nodules, with altered expression of several early nodulation genes. The expression levels of GmKAIs, and GmD14Ls were markedly changed in GmMAX2a mutant roots, so did their target repressor genes GmD53s and GmSMAX1s. Thus, SL and KAR signaling were involved in soybean–rhizobia interaction and nodulation partly through interactions with hormones, and this may explain the different effects of MXA2 orthologs on legume determinate and indeterminate nodulation. The study provides fresh insights into the roles of GmMAX2‐mediated SL/KAR signaling in soybean root hair and nodule formation.

Global dissection of the BAHD acyltransferase gene family in soybean: Expression profiling, metabolic functions, and evolution

“…The gene expression of BAHD members was analysed in RNA-Seq data derived from soybean nodules at different developing stages [1]. The results showed that BAHD genes were differentially expressed in the nodule at different developmental stages, from nodule development until its senescence ( Fig.…”

“…Samples at different nodulation stages (N-1 to N-6) were obtained [1]. The seedlings were hydroponically subjected to acidic treatment (pH 4.0) and 50 mM Al 3+ stress (under pH 4.0) [2,82] for 10 days before harvesting the roots for gene expression analysis.…”

Global dissection of the BAHD acyltransferase gene family in soybean: Expression profiling, metabolic functions, and evolution

“…From our analysis of RNA-Seq data derived from soybean nodules at different developing stages [78], BAHD genes were differentially expressed at different developmental stages of the nodule, since its development until senescence ( Fig. 7; Additional file 1: File S1b).…”

“…These nodules at different developmental stages can be marked by average dry weights, from N1 to N6 were about 0.0005, 0.001, 0.004, 0.01, 0.03, 0.07 gram. [85,78]. The seedlings were hydroponically subjected to acidic treatment (pH 4.0) and 50 mM Al 3+ stress (under pH 4.0) [15,89] for 10 days before harvesting the roots for expression analysis.…”

Comparing and Contrasting the Multiple Roles of Butenolide Plant Growth Regulators: Strigolactones and Karrikins in Plant Development and Adaptation to Abiotic Stresses

“…Similarly, the colonization of pea by arbuscular mycorrhizal resulted in a decrease in the germination rate of parasitic seeds due to a decrease in the content of SLs [130]. Moreover, arbuscular mycorrhizal colonization may inhibit the formation of legume nodules, due to the decrease in SL content [131]. For example, the root exudates of the SL-deficient rms1 mutant in pea have lower SL content and reduced nodulation capacity compared with the wild type, suggesting that SLs, as positive regulators of nodulation in peas, are necessary for optimal nodulation [118].…”