Developmental Analysis of the GATA Factor HANABA TARANU Mutants in Medicago truncatula Reveals Their Roles in Nodule Formation

Abstract

Formation of nodules on legume roots results from symbiosis with rhizobial bacteria. Here, we identified two GATA transcription factors, MtHAN1 and MtHAN2, in Medicago truncatula, which are the homologs of HANABA TARANU (HAN) and HANABA TARANU LIKE in Arabidopsis thaliana. Our analysis revealed that MtHAN1 and MtHAN2 are expressed in roots and shoots including the root tip and nodule apex. We further show that MtHAN1 and MtHAN2 localize to the nucleus where they interact and that single and double loss-of-function mutants of MtHAN1 and MtHAN2 did not show any obvious phenotype in flower development, suggesting their role is different than their closest Arabidopsis homologues. Investigation of their symbiotic phenotypes revealed that the mthan1 mthan2 double mutant develop twice as many nodules as wild type, revealing a novel biological role for GATA transcription factors. We found that HAN1/2 transcript levels respond to nitrate treatment like their Arabidopsis counterparts. Global gene transcriptional analysis by RNA sequencing revealed different expression genes enriched for several pathways important for nodule development including flavonoid biosynthesis and phytohormones. In addition, further studies suggest that MtHAN1 and MtHAN2 are required for the expression of several nodule-specific cysteine-rich genes, which they may activate directly, and many peptidase and peptidase inhibitor genes. This work expands our knowledge of the functions of MtHANs in plants by revealing an unexpected role in legume nodulation.

Regulation of the Later Stages of Nodulation Stimulated by IPD3/CYCLOPS Transcription Factor and Cytokinin in Pea Pisum sativum L.

“…Some GATA transcription factors were shown to be involved in symbiosis development in legume plants. The MtHAN1 and MtHAN2 genes encoding GATA transcription factors in M. truncatula are mainly expressed in the nodule primordia and in the infection zone in mature nodules, suggesting the participation of these transcription factors in nodulation [ 73 ]. The expression of genes encoding NCR peptides, responsible for bacteroid differentiation, is shown to be suppressed in han1 han2 double mutant [ 74 ].…”

Detection of type III effector‐induced transcription factors that regulate phytohormone content during symbiosis establishment in soybean

“…However, a prior study reported that nodulation is adversely impacted by the NopAA mutant, and this might be due to the different genetic background of the host legume (Almeida‐Trapp & Mithöfer, 2019; Okazaki et al, 2013). Furthermore, ABA and cytokinin act antagonistically to regulate nodule initiation in the root cortex (Wang et al, 2020; Xu, Song, et al, 2021; Xu, Wang, et al, 2021). Our results support that ABA is required to initiate rhizobium infection in soybean.…”