Abstract
BackgroundAbscisic acid (ABA) plays an important role in plant growth and adaptation through the ABA signaling pathway. The ABA-responsive element binding (AREB/ABF) family transcriptional factors are central regulators that integrate ABA signaling with various signaling pathways. It has long been known that ABA inhibits rhizobial infection and nodule formation in legumes, but the underlying molecular mechanisms remain elusive.ResultsHere, we show that nodulation is very sensitive to ABA and exogenous ABA dramatically inhibits rhizobial infection and nodule formation in soybean. In addition, we proved that GmbZIP1, an AREB/ABF transcription factor, is a major regulator in both nodulation and plant response to ABA in soybean. GmbZIP1 was specifically expressed during nodule formation and development. Overexpression of GmbZIP1 resulted in reduced rhizobial infection and decreased nodule number. Furthermore, GmbZIP1 is responsive to ABA, and ectopic overexpression of GmbZIP1 increased sensitivity of Arabidopsis plants to ABA during seed germination and postgerminative growth, and conferred enhanced drought tolerance of plants. Remarkably, we found that GmbZIP1 directly binds to the promoter of GmENOD40–1, a marker gene for nodule formation, to repress its expression.ConclusionOur results identified GmbZIP1 as a node regulator that integrates ABA signaling with nodulation signaling to negatively regulate nodule formation.
Highlights
Abscisic acid (ABA) plays an important role in plant growth and adaptation through the ABA signaling pathway
These results indicate that root nodule is the most sensitive organ of soybean to ABA during growth and development, and ABA plays a negative regulatory role in soybean nodulation
We showed that nodulation is the most sensitive process during plant growth and development; we identified GmbZIP1 as positive regulator of ABA response but negative regulator in soybean nodulation; and most importantly, we revealed that GmbZIP1 inhibits nodulation through directly repressing GmENOD40–1 expression
Summary
Abscisic acid (ABA) plays an important role in plant growth and adaptation through the ABA signaling pathway. NFs are perceived by Lysine motif receptor-like kinases (LysM) receptors (NFRs) located at plasma membrane of the epidermal cells of roots and root hairs These NF receptors include NF Perception (NFP) in M. truncatula, NF Receptors 1 and 5 (NFR1/5) in L. japonicus, SYM10/. Calcium oscillations in the nucleus is decoded by Calcium and Calmodulin-dependent Kinase (CCaMK in Lotus and DMI3 in Medicago) that form complex with CYCLOPS to activate a set of transcriptional factors [15, 16] These transcriptional factors include two GRAS domain transcriptional regulators [17,18,19,20,21], including Nodulation Signaling Pathway (NSP1) and NSP2, which can form a complex to directly activate expression of Nodule Inception (NIN), Ethylene Response Factor Required for Nodulation (ERN1) and Early Nodulin 11 (ENOD11) [22, 23]
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