Insights into role of STP13 in sugar driven signaling that leads to decrease in photosynthesis in dicot legume crop model (Phaseolus vulgaris L.) under Fe and Zn stress

Phaseolus vulgaris STP13.1 is an H+-coupled monosaccharide transporter, present in source leaves and seed coats, with higher substrate affinity at depolarized potentials

Sugar transport proteins (STPs) are high-affinity H+-coupled hexose symporters. Recently, the contribution of STP13 to bacterial and fungal pathogen resistance across multiple plant species has garnered significant interest. Quantitative PCR analysis of source leaves, developing embryos, and seed coats of Phaseolus vulgaris L. (common bean) revealed that PvSTP13.1 was expressed in source leaves and seed coats throughout seed development. In contrast, PvSTP13.1 transcripts were detected at exceedingly low levels in developing embryos. To characterize the transport mechanism, PvSTP13.1 was expressed in Xenopus laevis oocytes, and inward-directed currents were analyzed using two-electrode voltage clamping. PvSTP13.1 was shown to function as an H+-coupled monosaccharide symporter exhibiting a unique high affinity for hexoses and aldopentoses at depolarized membrane potentials. Specifically, of the 31 assessed substrates, which included aldohexoses, deoxyhexoses, fructose, 3-O-methyl-D-glucose, aldopentoses, polyols, glycosides, disaccharides, trisaccharides, and glucuronic acid, PvSTP13.1 displayed the highest affinity (K 0.5) for glucose (43 μM), mannose (92 μM), galactose (145 μM), fructose (224 μM), xylose (1.0 mM), and fucose (3.7 mM) at pH 5.6 at a depolarized membrane potential of -40 mV. The results presented here suggest PvSTP13.1 contributes to retrieval of hexoses from the apoplasmic space in source leaves and coats of developing seeds.

Genome-wide identification of sugar transporter gene family in Brassicaceae crops and an expression analysis in the radish

BACKGROUND

Sugar not only is an important biomacromolecule that plays important roles in plant growth, development, and biotic and abiotic stress tolerance but also provides a skeleton for other macromolecules, such as proteins and nucleic acids. Sugar transporter proteins (STPs) play essential roles in plant sugar transport and ultimately affect the abovementioned life processes. However, the evolutionary dynamics of this important gene family in Brassicaceae crops are still largely unknown, and the functional differentiation of radish STP genes remains unclear.

RESULTS

In the present study, a comparative genomic study of STP genes in five representative Brassicaceae crops was conducted, and a total of 25, 25, 28, 36 and 49 STP genes were individually identified in Raphanus sativus (Rs), Brassica oleracea (Bo), B. rapa (Br), B. napus (Bn) and B. juncea (Bj), which were divided into four clades by phylogenetic analysis. The number of STP genes was no direct correlation with genome size and the total number of coding genes in Brassicaceae crops, and their physical and chemical properties showed no significant difference. Expression analysis showed that radish STP genes play vital roles not only in flower and seedpod development but also under heavy metal (cadmium, chromium and lead), NaCl and PEG-6000 stresses, Agrobacterium tumefaciens infection, and exogenous sugar treatment. RsSTP13.2 was significantly upregulated in the resistant radish cultivar by A. tumefaciens infection and induced by heavy metal, NaCl and PEG-6000 stress, indicating that it is involved in resistance to both biotic and abiotic stress in radish.

CONCLUSIONS

The present study provides insights into the evolutionary patterns of the STP gene family in Brassicaceae genomes and provides a theoretical basis for future functional analysis of STP genes in Brassicaceae crops.

Fe and Zn stress induced gene expression analysis unraveled mechanisms of mineral homeostasis in common bean (Phaseolus vulgaris L.)

Iron (Fe) and zinc (Zn) stress significantly affects fundamental metabolic and physiological processes in plants that results in reduction of plant growth and development. In the present study, common bean variety; Shalimar French Bean-1 (SFB-1) was used as an experimental material. Four different MGRL media i.e. normal MGRL medium (Control), media without Fe (0-Fe), media without Zn (0-Zn) and media with excess Zn (300-Zn) were used for growing seeds of SFB-1 under in vitro condition for three weeks under optimum conditions. Three week old shoot and root tissues were harvested from the plants grown in these four different in vitro conditions and were, subjected to Fe and Zn estimation. Further, extraction of total RNA for differential gene expression of ten candidate genes selected based on our in silico investigation and their classification, phylogeny and expression pattern was unraveled. Expression analysis of three candidate genes (OPT3, NRAMP2 and NRAMP3) in roots revealed possible cross talk among Fe/Zn stress that was further confirmed by observing less accumulation of Fe in roots under both these conditions. However, we observed, higher accumulation of Fe in shoots under 0-Fe condition compared to control that suggests precise sensing for priority based compartmentalization and partitioning leading to higher accumulation of Fe in shoots. Furthermore, the expression analysis of IRT1, FRO1 and Ferritin 1 genes under Fe/Zn stress suggested their role in uptake/transport and signaling of Fe and Zn, whereas the expression of ZIP2, NRAMP1, HA2 and GLP1 genes were highly responsive to Zn in Phaseolus vulgaris. The identified genes highly responsive to Fe and Zn stress condition can be potential candidates for overcoming mineral stress in dicot crop plants.

Morphological, Biochemical, and Proteomic Studies Revealed Impact of Fe and P Crosstalk on Root Development in Phaseolus vulgaris L

Mineral stress is one of the major abiotic stresses faced by crop plants. The present study was undertaken to investigate the impact of mineral stress (iron (Fe) and phosphorus (P)) on various morphological and biochemical responses of the shoot and root tissues and root architecture of common bean (Phaseolus vulgaris L.). This study also leads us to the identification of P stress responsive proteins. The study was conducted under in vitro conditions, in which seeds of Shalimar French Bean-1 (SFB-1) variety were cultured on four different MGRL medium (control (P₁Fe₁), iron deficient (P₁Fe₀), phosphorus deficient (P₀Fe₁), and phosphorus and iron deficient (P₀Fe₀)). Chlorophyll content of leaves, Fe/P content of root tissues, total sugars, proline, length, and weight of shoot and root tissues were assessed and compared within and between the treatments. The analyzed data revealed significant difference between control and other three treatments. Chlorophyll content of shoots was found significantly decreased under mineral stress treatments P₀Fe₁, P₁Fe₀, and P₀Fe₀ than control. Length and weight of shoot and root were also observed significantly decreased under P₀Fe₁, P₁Fe₀, and P₀Fe₀ as compared to control. Total sugar was significantly higher in P₀Fe₁ of roots in comparison to control. Proline content was significantly higher in both tissues of shoots and roots of plants grown under P₁Fe₀, P₀Fe₁, and P₀Fe₀ than control condition. Furthermore, we unexpectedly observed the recovery of roots (mainly primary roots) under P₀Fe₀ as compared to P₁Fe₀ and P₀Fe₁^. Interestingly higher concentration of Fe was also observed in P₀Fe₁ compared to other treatments and also higher concentration of P was observed in P₁Fe₁. These findings suggested that there is a crosstalk between Fe and P and also revealed that there is a disruption in the ability of PR (primary root) to sense local P deficiency in the absence of Fe. Furthermore, proteomics analysis (SDS-PAGE followed by MALDI MS) helped in identification of defensive proteins in P stress condition compared to control.