Abstract
Fabaceans produce two major classes of symbiotic nodules: the indeterminate type characterized by a persistent meristem, and the determinate type that lacks a persistent meristem. The class III homeodomain leucine zipper (HD-ZIP III) transcription factor family influence development of multiple lateral organs and meristem maintenance, but their role in determinate nodule development is not known. HD-ZIP III protein activity is post-translationally regulated by members of the small leucine zipper protein (ZPR) family in arabidopsis. We characterized the ZPR gene family in soybean and evaluated their ability to interact with two key members of GmHD-ZIP III family through yeast two-hybrid assays. GmZPR3d displayed the strongest interaction with GmHD-ZIP III-2 among the different pairs evaluated. GmHD-ZIP III-1, -2, and GmZPR3d showed overlapping expression patterns in the root stele and in nodule parenchyma tissues. Over-expression of GmZPR3d resulted in ectopic root secondary xylem formation, and enhanced expression of vessel-specific master switch genes in soybean. The nodules in ZPR3d over-expressing roots were larger in size, had a relatively larger central zone and displayed increased nodule vascular branching. The results from this study point to a key role for GmZPR3d in soybean root and nodule development.
Highlights
Class III homeodomain leucine zipper proteins (HD-ZIP IIIs) are plant specific transcription factors and are key players in multiple developmental processes beginning from embryo development to plant maturity in Arabidopsis and other plant species [1,2,3]
Interaction between Arabidopsis zipper protein (ZPR) and HD-ZIP III proteins have been evaluated through yeast two-hybrid and in vitro pull-down assays [19,36]
We identified eight soybean ZPR orthologs and evaluated their interactions with GmHD-ZIPIII-1 and GmHD-ZIPIII-2 using yeast two-hybrid assays
Summary
Class III homeodomain leucine zipper proteins (HD-ZIP IIIs) are plant specific transcription factors and are key players in multiple developmental processes beginning from embryo development to plant maturity in Arabidopsis and other plant species [1,2,3]. Several loss- or and gain-of-function mutants of these genes have been shown to affect shoot apical meristem (SAM) and lateral organ polarity [7]. Role of ATHB15 in root development was discovered with the gain of function allele icu. Role of ATHB15 in root development was discovered with the gain of function allele icu4-1 This mutant has a disorganized root meristem with excess cells around the quiescent center (QC) and an increased number of lateral roots. The triple loss of function mutant phb-6/phv-5/rev-9 shows reduced number of lateral roots [1]. All these studies clearly indicated a role for HD-ZIP IIIs in vascular development and lateral organ formation
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