Control of the Rhizobia Nitrogen-Fixing Symbiosis by Common Bean MADS-Domain/AGL Transcription Factors

Plants MADS-domain/AGL proteins constitute a large transcription factor (TF) family that controls the development of almost every plant organ. We performed a phylogeny of (ca. 500) MADS-domain proteins from Arabidopsis and four legume species. We identified clades with Arabidopsis MADS-domain proteins known to participate in root development that grouped legume MADS-proteins with similar high expression in roots and nodules. In this work, we analyzed the role of AGL transcription factors in the common bean (Phaseolus vulgaris) – Rhizobium etli N-fixing symbiosis. Sixteen P. vulgaris AGL genes (PvAGL), out of 93 family members, are expressed – at different levels – in roots and nodules. From there, we selected the PvAGL gene denominated PvFUL-like for overexpression or silencing in composite plants, with transgenic roots and nodules, that were used for phenotypic analysis upon inoculation with Rhizobium etli. Because of sequence identity in the DNA sequence used for RNAi-FUL-like construct, roots, and nodules expressing this construct -referred to as RNAi_AGL- showed lower expression of other five PvAGL genes highly expressed in roots/nodules. Contrasting with PvFUL-like overexpressing plants, rhizobia-inoculated plants expressing the RNAi_AGL silencing construct presented affection in the generation and growth of transgenic roots from composite plants, both under non-inoculated or rhizobia-inoculated condition. Furthermore, the rhizobia-inoculated plants showed decreased rhizobial infection concomitant with the lower expression level of early symbiotic genes and increased number of small, ineffective nodules that indicate an alteration in the autoregulation of the nodulation symbiotic process. We propose that the positive effects of PvAGL TF in the rhizobia symbiotic processes result from its potential interplay with NIN, the master symbiotic TF regulator, that showed a CArG-box consensus DNA sequence recognized for DNA binding of AGL TF and presented an increased or decreased expression level in roots from non-inoculated plants transformed with OE_FUL or RNAi_AGL construct, respectively. Our work contributes to defining novel transcriptional regulators for the common bean – rhizobia N-fixing symbiosis, a relevant process for sustainable agriculture.

Production and analysis of tomato Solanum lycopersicum composite plants carrying the genes of pea Pisum sativum receptors to rhizobial signaling molecules

The interaction of composite tomato plants carrying constructs with pea genes encoding receptors to Nod factors, with nitrogen-fixing bacteria rhizobia was investigated.

Methodological approaches to agrobacterium-mediated transformation of buckwheat (Fagopyrum esculentum Moench)

The method of Agrobacterium rhizogenes-mediated transformation of buckwheat has been established; composite plants have been obtained. The distribution of the cellular response to auxin by reporter proteins with different maturation times coincides.

Composite plants for a composite plant: An efficient protocol for root studies in the sunflower using composite plants approach

Sunflower (Helianthus annuus L.) is important oilseed crop in the world and the sunflower oil is prized for its’ exceptional quality and flavor. The recent availability of the sunflower genome can allow genome-wide characterization of genes and gene families. With plant transformation usually being the rate limiting step for gene functional studies of sunflower, composite plants can alleviate this bottleneck. Composite plants, produced using Agrobacterium rhizogenes, are plants with transgenic roots and wild type shoots. Composite plants offer benefits over creating fully transgenic plants, namely time and cost. Here we outlined the critical steps and parameters for a protocol for the sunflower composite plants production. We use more than a dozen genotypes and three constitutive promoters to validates the utility and efficiency of this protocol. Moreover, functional gene characterization by overexpression and RNAi silencing of a root related transcription factor HaLBD16 further emphasize the value of the system in the sunflower studies. With the protocol developed here an experiment can be carried out with efficiency and in only two months. This procedure adds to arsenal of approaches for the functional genetics/genomics in sunflower for characterization candidate genes involved in root development and stress adaptation.Key messageComposite plants technique described here is fast and efficient approach for roots functional studies in sunflower.

Grafting influence on productivity and drought tolerance of tea clones

Grafting of fresh cuttings using drought-susceptible and low-yielding clones as scions on drought-tolerant clones as rootstocks offers the possibility of raising composite plants with improved productivity and drought tolerance. Hence, the study was aimed to widen the choice of compatible composites and to delineate the underlying factors responsible for productivity and drought tolerance in grafted plants. One year-old composite plants of TRF-1, TRF-2 and UPASI-28 cleft-grafted on the rootstocks of UPASI-2, UPASI-9, ATK-1 and TRI-2025 were field planted along with their respective controls and evaluated. The results indicated that productivity and drought tolerance of scion clones varied significantly with the rootstocks used. Significant increases in yield and yield components were noted in the following graft combinations compared with their corresponding self-rooted scion clones: TRF-1 grafted on UPASI-9 and ATK-1, TRF-2 grafted on all four rootstocks, and UPASI-28 grafted on UPASI-9, TRI-2025 and UPASI-2. The findings clearly emphasize the scion–rootstock interaction as the critical determinant of productivity in grafted plants compared with vigour, drought tolerance and yield potential of scion and rootstock clones. Further, high-yielding capacity of grafts over the ungrafted scions and rootstocks was largely dependent on the yield potential of the scion clone and the degree of scion–rootstock compatibility. Higher field survival and enhanced yield observed during the drought period in the compatible grafts demonstrated their better drought tolerance compared with their respective self-rooted scions.