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Drought is a major limiter of yield in common bean, decreasing food security for those who rely on it as an important source of protein. While drought can have large impacts on yield by reducing photosynthesis and therefore resources availability, source strength is not a reliable indicator of yield. One reason resource availability does not always translate to yield in common bean is because of a trait inherited from wild ancestors. Wild common bean halts growth and seed filling under drought and awaits better conditions to resume its developmental program. This trait has been carried into domesticated lines, where it can result in strong losses of yield in plants already producing pods and seeds, especially since many domesticated lines were bred to have a determinate growth habit. This limits the plants ability to produce another flush of flowers, even if the first set is aborted. However, some bred lines are able to maintain higher yields under drought through maintaining growth and seed filling rates even under water limitations, unlike their wild predecessors. We believe that maintenance of sink strength underlies this ability, since plants which fill seeds under drought maintain growth of sinks generally, and growth of sinks correlates strongly with yield. Sink strength is determined by a tissue’s ability to acquire resources, which in turn relies on resource uptake and metabolism in that tissue. Lines which achieve higher yields maintain higher resource uptake rates into seeds and overall higher partitioning efficiencies of total biomass to yield. Drought limits metabolism and resource uptake through the signaling molecule abscisic acid (ABA) and its downstream affects. Perhaps lines which maintain higher sink strength and therefore higher yields do so through decreased sensitivity to or production of ABA.

Auxin-regulated transcription pivots on the interaction between the AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) repressor proteins and the AUXIN RESPONSE FACTOR (ARF) transcription factors. Recent structural analyses of ARFs and Aux/IAAs have raised questions about the functional complexes driving auxin transcriptional responses. To parse the nature and significance of ARF–DNA and ARF–Aux/IAA interactions, we analyzed structure-guided variants of synthetic auxin response circuits in the budding yeast Saccharomyces cerevisiae. Our analysis revealed that promoter architecture could specify ARF activity and that ARF19 required dimerization at two distinct domains for full transcriptional activation. In addition, monomeric Aux/IAAs were able to repress ARF activity in both yeast and plants. This systematic, quantitative structure-function analysis identified a minimal complex—comprising a single Aux/IAA repressing a pair of dimerized ARFs—sufficient for auxin-induced transcription.

Throughout development, plants are constantly shifting resource allocation between their different tissue types; roots, stems, leaves, fruits and seeds. This allows them to balance resource gain, optimize growth, and increase reproductive output. While plants with different life history strategies have evolved very different patterns of allocation (ie. perennials conserve resources for the next year while annuals put all available resources into the next generation), the overall goal of increasing fitness underlies their behaviors. Still, it is not well understood what determines resource allocation into reproductive structures, specifically seeds. It’s clear that carbon availability and developmental processes play a crucial role - flowers, fruits and seeds must be produced, but a priority of allocation towards these structures must also be established and maintained to ensure high reproductive output.Drought is a significant factor which can impact allocation processes and seed filling. This can be due to changes in resource availability, as drought commonly decreases photosynthesis. However, allocation processes themselves are known to be affected by drought via signaling, particularly through the phytohormone abscisic acid. This means that even when resources themselves do not limit allocation and growth potential, other processes such as resource uptake into or metabolism within growing tissues may be slowed. Allocation processes therefore may be halted under drought stress, ultimately leading to decreased growth and/or seed filling. However, the degree to which different species and even different genotypes of a single species are impacted by drought differs strongly, resulting in some plants being better able to maintain allocation processes under drought. Lines which achieve this are deemed to be drought-tolerant.What allows drought-tolerant genotypes to maintain allocation and seed filling under drought? We set out to answer this question using common bean (Phaseolus vulgaris), where drought-tolerant lines have been shown to maintain higher allocation rates. Our goal was to gain a better understanding of the physiological underpinnings which control differences in allocation between drought-tolerant and drought-sensitive common bean lines. To begin, we tested how allocation processes, generally, were affected in tolerant and sensitive lines. We wondered if allocation to seeds was impacted by drought, would allocation towards any sink tissue be interrupted by drought? We found that within a genotype, drought’s impacts to growth and allocation acted in a consistent way across different sink tissues, such as leaves and seeds. That is, genotypes which had leaf growth strongly depressed by drought also had seed growth strongly depressed. This was not shown to be tightly correlated with resource availability or water status within the plant. Conversely, genotypes which maintained a high growth rate in one sink tissue, retained higher growth in other sinks. Genotypes which achieved higher growth resulted in a faster maturation of seeds, effectively allowing these lines to avoid potentially worsening drought.To better understand the differences in allocation between drought sensitive and drought tolerant lines, we quantified allocation across the different tissues of a plant over reproductive development. We found that drought-tolerant common bean lines (1) allocated biomass to seeds earlier, (2) allocated a larger percentage of total biomass to seeds than drought-sensitive lines, allowing the tolerant lines to achieve the same absolute yield as the sensitive line even with less total biomass, and (3) did not alter their seed filling profile under water stress, meaning the developmental program of seed filling was not altered by drought. In contrast, the sensitive line did have different seed filling profile under well-watered and water stressed. This suggests that the sensitive line alters development under drought whereas the tolerant does not.We believe that maintenance of allocation and therefore growth in the drought-tolerant line is the direct result of maintaining what is known as ‘sink strength’. Sink strength is defined as the ability of a growing, sink tissue, to obtain resources for use within the sink. Many mechanisms are known to be involved in setting sink strength, including resource uptake via transporters, proton pump and enzyme levels and activity. Proton pumps work to establish gradients across the membrane to drive resource uptake via transporters, and enzymes are involved in the breakdown and metabolism of materials, allowing for their transport into and use within sinks.We found that differences in these processes between genotypes determined differences in allocation and growth rate. When common bean seeds were floated in growth media containing sugar, uptake rates and growth were genotype and condition specific, rather than related to the concentration of sugar in the growth medium. This points to the seed itself as the point of regulation driving differences in seed filling.What underlies differences in the drought-tolerant line and the drought-sensitive line may be related to drought sensitivity, particularly to the hormone mentioned above, abscisic acid (ABA). We found that the drought-tolerant lines did not change the seed filling profile, nor seed filling rate or acidification rates in in vitro assays when exposed to drought and ABA, respectively. The drought sensitive line however did change its seed filling profile, seed filling rate and acidification rate under drought. Therefore, we believe that tolerant lines may have impaired drought sensitivity. This is perhaps through a reduced ability to produce, sense or respond to ABA, or potentially ABA production or sensing is constitutively on. However this is achieved, reduced drought sensitivity results in plants which maintain allocating resources towards sinks, importantly seeds, under drought stress. This allows them to fill seeds faster and increase the percent of total biomass allocated to seeds, increasing yields under drought.

While drought limits yield largely by its impact on photosynthesis and therefore biomass accumulation, biomass is not the strongest predictor of yield under drought. Instead, resource partitioning efficiency, measured by how much total pod weight is contained in seeds at maturity (Pod Harvest Index), is the stronger correlate in Phaseolus vulgaris. Using 20 field-grown genotypes, we expanded on this finding by pairing yield and resource partitioning data with growth rates of leaflets and pods. We hypothesized that genotypes which decreased partitioning and yield most under drought would also have strongest decreases in growth rates. We found that while neither leaflet nor pod growth rates correlated with seed yield or partitioning, impacts to leaflet growth rates under drought correlate with impacts to yield and partitioning. As expected, biomass production correlated with yield, yet correlations between the decreases to these two traits under drought were even stronger. This suggests that while biomass contributes to yield, biomass sensitivity to drought is a stronger predictor. Lastly, under drought, genotypes may achieve similar canopy biomass yet different yields, which can be explained by higher or lower partitioning efficiencies. Our findings suggest that inherent sensitivity to drought may be used as a predictor of yield.

An intractable challenge in glaucoma treatment has been to identify druggable targets within the conventional aqueous humor outflow pathway, which is thought to be regulated/dysregulated by elusive mechanosensitive protein(s). Here, biochemical and functional analyses localized the putative mechanosensitive cation channel TRPV4 to the plasma membrane of primary and immortalized human TM (hTM) cells, and to human and mouse TM tissue. Selective TRPV4 agonists and substrate stretch evoked TRPV4-dependent cation/Ca 2+ influx, thickening of F-actin stress fibers and reinforcement of focal adhesion contacts. TRPV4 inhibition enhanced the outflow facility and lowered perfusate pressure in biomimetic TM scaffolds populated with primary hTM cells. Systemic delivery, intraocular injection or topical application of putative TRPV4 antagonist prodrug analogs lowered IOP in glaucomatous mouse eyes and protected retinal neurons from IOP-induced death. Together, these findings indicate that TRPV4 channels function as a critical component of mechanosensitive, Ca 2+ -signaling machinery within the TM, and that TRPV4-dependent cytoskeletal remodeling regulates TM stiffness and outflow. Thus, TRPV4 is a potential IOP sensor within the conventional outflow pathway and a novel target for treating ocular hypertension.

Background. Pre-exposure prophylaxis (PrEP) is an effective prevention tool for people at substantial risk of acquiring human immunodeficiency virus (HIV). To monitor the current state of PrEP use among men who have sex with men (MSM), we report on willingness to use PrEP and PrEP utilization. To assess whether the MSM subpopulations at highest risk for infection have indications for PrEP according to the 2014 clinical guidelines, we estimated indications for PrEP for MSM by demographics. Methods. We analyzed data from the 2014 cycle of the National HIV Behavioral Surveillance (NHBS) system among MSM who tested HIV negative in NHBS and were currently sexually active. Adjusted prevalence ratios and 95% confidence intervals were estimated from log-linked Poisson regression with generalized estimating equations to explore differences in willingness to take PrEP, PrEP use, and indications for PrEP. Results. Whereas over half of MSM said they were willing to take PrEP, only about 4% reported using PrEP. There was no difference in willingness to take PrEP between black and white MSM. PrEP use was higher among white compared with black MSM and among those with greater education and income levels. Young, black MSM were less likely to have indications for PrEP compared with young MSM of other races/ethnicities. Conclusions. Young, black MSM, despite being at high risk of HIV acquisition, may not have indications for PrEP under the current guidelines. Clinicians may need to consider other factors besides risk behaviors such as HIV incidence and prevalence in subgroups of their communities when considering prescribing PrEP.