Comparative analysis of infection process in Pima cotton differing in resistance to Fusarium wilt caused by Fusarium oxysporum f. sp. vasinfectum race 4

Fusarium oxysporum f. sp. vasinfectum race 4 (FOV4) causes an early season cotton disease including seedling deaths. This study compared two Pima cottons (Gossypium barbadense) in the infection process of FOV4 using a confocal and a scanning electron microscope. Seedlings were grown in a hydroponic system and inoculated with a virulent local FOV4 isolate. As compared to the susceptible Pima S-7, the resistant Pima PHY 841 RF had significantly fewer conidia attached and germinated on the root surface. FOV4 penetration into the root epidermis of PHY 841 RF was delayed until 24 hours post-inoculation (hpi), as compared to 8 hpi in Pima S-7. In Pima S-7, hyphae progressed to the xylem through the cortex between 5 and 7 days post-inoculation. However, hyphae grew much slower in the cortex with no apparent hyphae observed in the xylem of PHY 841 RF. At plant maturity, no FOV4 was detected through fungal isolation and PCR in the stem of PHY 841 RF and its resistance donor parents PHY 800 and Pima S-6, as compared to Pima S-7 and DP 744 with positive results.

Isolation of Rhizosheath and Analysis of Microbial Community Structure Around Roots of Stipa Grandis

Background：The root zone microbial structure is particularly complex for plants with rhizosheaths, which may play an important role in the future agricultural sustainable development. However, one of the important reasons for restricting our study of rhizosheath microbial structure is that there is no definite method for rhizosheath separation. The aim of this study was to explore the isolation methods of rhizosheath and the diversity characteristics of microorganisms around the rhizosphere. In this study, we isolated the rhizosheath of Stipa grandis, a dominant species in desert steppe, and the microorganisms in the roots, root epidermis, rhizosheath, rhizosphere soil were extracted and sequenced by 16SrRNA and ITS.Results:The bacterial alpha diversity index was in the order rhizosphere soil > rhizosheath>root epidermis>endophytic, and the fungal alpha diversity index wasrhizosphere soil and rhizosheath> root epidermisand endophytic. There were significant differences in bacterial community structure between the root epidermis and endophytic, rhizosheath, rhizosphere soil. Different from bacterial community structure, the community structure of root epidermis fungi was similar to endophytic, but significantly different from rhizosheath and rhizosphere soil.Our method is feasible for separating plant rhizosheath and root epidermis.Conclusions：We suggest that the root epidermiscan act as the interface between the host plant root and the external soil environment.We will have to re-examine the biological and ecological significance of root sheath and microorganisms in rhizosheath, as well as the mechanism of its close relationship with plant root epidermis.This study will provide theoretical and technical guidance for the isolation of plant rhizosheath and the study of microorganisms in it.

Supra-physiological levels of gibberellins/DELLAs modify the root cell size/number and the root architecture in root tips of A. thaliana seedlings. Connections to the root hair patterning and abundance

A previous study (McCarthy-Suarez, 2021) showed that growing A. thaliana seedlings for 5 days under excessive levels of gibberellins (GAs)/DELLAs altered the arrangement, shape and frequency of root hairs in root tips. Because no changes in the distribution or number of root hairs occurred when the gai-1 (gibberellin-insensitive-1) DELLA was over-expressed at the root epidermis, it was concluded that the GAs/DELLAs might regulate the root hair patterning and abundance in A. thaliana seedlings by acting from the root sub-epidermal tissues. In the present study, microscopy analyses showed that excessive levels of GAs/DELLAs also modified the size and number of root tip cells in A. thaliana seedlings. While excessive DELLAs shortened and widened the root epidermal, cortical, endodermal and pericycle cells, excessive GAs, excepting the epidermal cells, generally narrowed them. However, no changes of root cell size occurred when gai-1 was over-expressed at the root epidermis. In addition, high levels of DELLAs often induced extra cells at the root epidermis, cortex, endodermis and pericycle, whereas high levels of GAs sometimes induced extra cells at the root cortex and pericycle. On the other hand, excessive levels of DELLAs enhanced the outgrowth of lateral roots in root tips, unlike excessive levels of GAs. Thus, the results of this study suggest that supra-physiological levels of GAs/DELLAs might modify the size/number of root tip cells by acting from the root sub-epidermal tissues. This, in turn, might impact on the patterning and abundance of root hairs and on the root architecture.

Supra-physiological levels of Gibberellins/DELLAs alter the patterning, morphology and abundance of root hairs in root tips of A. thaliana seedlings

In spite of the known role of gibberellins (GAs), and of their antagonistic proteins, the DELLAs, in leaf hair production, no investigations, however, have assessed their hypothetical function in the production of root hairs. To this aim, the effects of supra-physiological levels of GAs/DELLAs on the spatial patterning of gene expression of the root hair (CPC) and root non-hair (GL2, EGL3 and WER) epidermal cell fate markers, as well as on the distribution, morphology and abundance of root hairs, were studied in root tips of 5-day-old A. thaliana seedlings. Results showed that excessive levels of GAs/DELLAs impaired the spatial patterning of gene expression of the root hair/non-hair epidermal cell fate markers, as well as the arrangement, shape and frequency of root hairs, giving rise to ectopic hairs and ectopic non-hairs, two-haired cells, two-tipped hairs, branched hairs, longer and denser hairs near the root tip under excessive DELLAs, and shorter and scarcer hairs near the root tip under excessive GAs. However, when the gai-1 (GA-insensitive-1) DELLA mutant protein was specifically over-expressed at the root epidermis, no changes in the patterning or abundance of root hairs occurred. Thus, these results suggest that, in seedlings of A. thaliana, the GAs/DELLAs might have a role in regulating the patterning, morphology and abundance of root hairs by acting from the sub-epidermal tissues of the root.

3,4-dehydro-L-proline Induces Programmed Cell Death in the Roots of Brachypodium distachyon

As cell wall proteins, the hydroxyproline-rich glycoproteins (HRGPs) take part in plant growth and various developmental processes. To fulfil their functions, HRGPs, extensins (EXTs) in particular, undergo the hydroxylation of proline by the prolyl-4-hydroxylases. The activity of these enzymes can be inhibited with 3,4-dehydro-L-proline (3,4-DHP), which enables its application to reveal the functions of the HRGPs. Thus, to study the involvement of HRGPs in the development of root hairs and roots, we treated seedlings of Brachypodium distachyon with 250 µM, 500 µM, and 750 µM of 3,4-DHP. The histological observations showed that the root epidermis cells and the cortex cells beneath them ruptured. The immunostaining experiments using the JIM20 antibody, which recognizes the EXT epitopes, demonstrated the higher abundance of this epitope in the control compared to the treated samples. The transmission electron microscopy analyses revealed morphological and ultrastructural features that are typical for the vacuolar-type of cell death. Using the TUNEL test (terminal deoxynucleotidyl transferase dUTP nick end labelling), we showed an increase in the number of nuclei with damaged DNA in the roots that had been treated with 3,4-DHP compared to the control. Finally, an analysis of two metacaspases’ gene activity revealed an increase in their expression in the treated roots. Altogether, our results show that inhibiting the prolyl-4-hydroxylases with 3,4-DHP results in a vacuolar-type of cell death in roots, thereby highlighting the important role of HRGPs in root hair development and root growth.

Analysis of Microbial Community Structure Around Roots of Stipa Grandis

The root zone microbial structure is particularly complex for plants with rhizosheaths, which may play an important role in the future agricultural sustainable development. However, one of the important reasons for restricting our study of rhizosheath microbial structure is that there is no definite method for rhizosheath separation. The aim of this study was to explore the isolation methods of rhizosheath and the diversity and functional characteristics of microorganisms around the rhizosphere. In this study, we isolated the rhizosheath of Stipa grandis, a dominant species in desert steppe, and the microorganisms in the roots, root epidermis, rhizosheath, rhizosphere soil were extracted and sequenced by 16s RNA and ITS. The bacterial alpha diversity index was in the order rhizosphere soil > rhizosheath > root epidermis > endophytic, and the fungal alpha diversity index was rhizosphere soil and rhizosheath > root epidermis and endophytic. There were significant differences in bacterial community structure between the root epidermis and endophytic, rhizosheath, rhizosphere soil, and the sum of relative abundance of the dominant bacterial populations Actinobacteria and Proteobacteria was 73.9% in the root epidermis. Different from bacterial community structure, the community structure of root epidermis fungi was similar to endophytic, but significantly different from rhizosheath and rhizosphere soil. We suggest that the root epidermis can act as the interface between the host plant root and the external soil environment. This study will provide theoretical and technical guidance for the isolation of plant rhizosheath and the study of microorganisms in it.

Character changes and Transcriptomic analysis of a cassava sexual Tetraploid

Background Cassava (Manihot esculenta Crantz) is an important food crop known for its high starch content. Polyploid breeding is effective in its genetic improvement, and use of 2n gametes in sexual polyploid breeding is one of the potential methods for cassava breeding and improvement. In our study, the cassava sexual tetraploid (ST), which carries numerous valuable traits, was successfully generated by hybridizing 2n female gametes SC5 (♀) and 2n male gametes SC10 (♂). However, the molecular mechanisms remain unclear. To understand these underlying molecular mechanisms behind the phenotypic alterations and heterosis in ST plants, we investigated the differences in gene expression between polyploids and diploids by determining the transcriptomes of the ST plant and its parents during the tuber root enlargement period. We also compared the characters and transcriptomes of the ST plant with its parents. Results The ST plant was superior in plant height, stem diameter, leaf area, petiole length, plant weight, and root weight than the parent plants, except the leaf number, which was lower. The number of starch granules was higher in the roots of ST plants than those in the parent plants after five months (tuber root enlargement period), which could be due to a higher leaf net photosynthetic rate leading to early filling of starch granules. Based on transcriptome analysis, we identified 2934 and 3171 differentially expressed genes (DEGs) in the ST plant as compared to its female and male parents, respectively. Pathway enrichment analyses revealed that flavonoid biosynthesis and glycolysis/gluconeogenesis were significantly enriched in the ST plants, which might contribute to the colors of petiole (purple-red), root epidermis (dark brown), and tuber starch accumulation, respectively. Conclusions After sexual polyploidization, the phenotype of ST has changed significantly in comparison to their diploid parents, mainly manifest as enlarged biomass, yield, early starch filling, deep colored petiole and root epidermis. The tetraploid plants were also mature early due to early starch grain filling. Owing to enriched flavonoid biosynthesis and glycolysis/gluconeogenesis, they are possibly resistant to adversity stresses and provide better yield, respectively.

Abscisic Acid Regulates the Root Growth Trajectory by Reducing Auxin Transporter PIN2 Protein Levels in Arabidopsis thaliana

The root is in direct contact with soil. Modulation of root growth in response to alterations in soil conditions is pivotal for plant adaptation. Extensive research has been conducted concerning the adjustment of root elongation and architecture in response to environmental factors. However, little is known about the modulation of the root growth trajectory, as well as its hormonal mechanism. Here we report that abscisic acid (ABA) participated in controlling root growth trajectory. The roots upon ABA treatment or from ABA-accumulation double mutant cyp707a1,3 exhibit agravitropism-like growth pattern (wavy growth trajectory). The agravitropism-like phenotype is mainly ascribed to the compromised shootward transportation of auxin since we detected a reduced fluorescence intensity of auxin reporter DR5:VENUS in the root epidermis upon exogenous ABA application or in the endogenous ABA-accumulation double mutant cyp707a1,3. We then tried to decipher the mechanism by which ABA suppressed shootward auxin transport. The membrane abundance of PIN2, a facilitator of shootward auxin transport, was significantly reduced following ABA treatment and in cyp707a1,3. Finally, we revealed that ABA reduced the membrane PIN2 intensity through suppressing the PIN2 expression rather than accelerating PIN2 degradation. Ultimately, our results suggest a pivotal role for ABA in the root growth trajectory and the hormonal interactions orchestrating this process.

Genetics of Orange, Red and Yellow Root Colours in Tropical Carrots (Dacus Carota L.)

The research was carried out to study the colour inheritance genetics of the root epidermis, core (phloem) and cortex (xylem), from the parental crosses of the varieties Pusa Meghali (Orange), Pusa Rudhira (Red) and Pusa Kulfi (Yellow). Resultant in crosses yielded uniform mixed colours in F1 (first filial generation), thus could enhance the security of human nutrition through the mixture of carotenoids and anthocyanins in the F1. The F1s were advance to produce F2 and backcross (BCP1 and BCP2) generations, and the Chi-square test ratio (χ2) showed that the root colour of the orange epidermis and cortex (xylem) was dominant over the red and yellow colours, and regulated by dominant genes Oe and Ocx from the parent Pusa Meghali. While, the root colour of the orange core (phloem) was found to be recessive to the red (Rc) from Pusa Rudhira and yellow (Yc) colour from Pusa Kulfi, and to be regulated by a single recessive gene (oc) from the parent Pusa Meghali. These finding of genetic inheritance of colours would be useful in the development of bio-fortified F1 hybrids and varieties which are rich in flavonoids.