Perturbation of tonoplast sucrose transport alters carbohydrate utilization for seasonal growth and defense metabolism in coppiced poplar.

Nonstructural carbohydrate reserves of stems and roots underpin overall tree fitness and productivity under short-rotation management practices such as coppicing for bioenergy. While sucrose and starch comprise the predominant stem carbohydrate reserves of Populus, utilization for fitness and agricultural productivity is understood primarily in terms of starch turnover. The tonoplast sucrose transport protein SUT4 modulates sucrose export from source leaves to distant sinks during photoautotrophic growth, but the possibility of its involvement in remobilizing carbohydrates from storage organs during heterotrophic growth has not been explored. Here, we used PtaSUT4-knockout mutants of Populus tremula × P. alba (INRA 717-1B4) in winter (cool) and summer (warm) glasshouse coppicing experiments to assess SUT4 involvement in reserve utilization. Conditions preceding and supporting summer sprouting were considered favorable for growth, while those preceding and supporting cool temperature sprouting were suboptimal akin to conditions associated with coppicing as generally practiced. Epicormic bud emergence was delayed in sut4 mutants following lower temperature 'winter' but not summer coppicing. Winter xylem hexose increases were observed in control but not in sut4 stumps after coppicing. The magnitude of starch and sucrose reserve depletion was similar in control and sut4 stumps during the winter and did not explain the sprouting and xylem hexose differences. However, winter maintenance costs appeared higher in sut4 based partly on Krebs cycle intermediate levels. In control plants, bark accrual of abundant defense metabolites, including salicinoids and condensed tannins, was higher in summer than in winter, but this increase of summer defense allocations was attenuated in sut4 mutants. Temperature-sensitive trade-offs between growth and other priorities may therefore depend on SUT4 in Populus.

Development of the Mentoring in Undergraduate Research Survey.

Here we present the development of the Mentoring in Undergraduate Research Survey (MURS) as a measure of a range of mentoring experienced by undergraduate science researchers. We drafted items based on qualitative research and refined the items through cognitive interviews and expert sorting. We used one national dataset to evaluate the internal structure of the measure and a second national dataset to examine how responses on the MURS related to theoretically relevant constructs and student characteristics. Our factor analytic results indicate seven lower order forms of mentoring experiences: abusive supervision, accessibility, technical support, psychosocial support, interpersonal mismatch, sexual harassment, and unfair treatment. These forms of mentoring mapped onto two higher-order factors: supportive and destructive mentoring experiences. Although most undergraduates reported experiencing supportive mentoring, some reported experiencing absence of supportive as well as destructive experiences. Undergraduates who experienced less supportive and more destructive mentoring also experienced lower scientific integration and a dampening of their beliefs about the value of research. The MURS should be useful for investigating the effects of mentoring experienced by undergraduate researchers and for testing interventions aimed at fostering supportive experiences and reducing or preventing destructive experiences and their impacts.

What Makes a Good Match? Predictors of Quality Mentorship Among Doctoral Students.

Quality mentoring promotes graduate student success. Despite an abundance of practical advice, empirical evidence regarding how to match mentees and mentors to form quality mentoring relationships is lacking. Here, we examine the influence of variables theorized to predict mentorship support and quality in a national sample of 565 science doctoral students from 70 universities in 38 states. Our structural equation modeling results indicate that mentor rank, mentee capital, and the relationship matching mechanism (direct admissions, rotations) were not associated with higher-quality relationships. We found no support for the widely held belief that students whose mentors shared their gender, race, or ethnicity experienced greater mentorship quality. Rather, mentees who shared attitudes, beliefs, and values with their mentor, or whose mentors displayed greater cultural awareness experienced more supportive, higher quality mentoring. Furthermore, these patterns were largely consistent across both mentee and mentor demographic groups. These results highlight the potential benefits of pairing mentees and mentors who share personal and intrinsic qualities rather than demographic or surface-level attributes. Our findings also indicate that graduate students from marginalized backgrounds can be effectively mentored by faculty who are demographically dissimilar if their mentors engage in culturally aware mentorship.

Tonoplast Sucrose Trafficking Modulates Starch Utilization and Water Deficit Behavior in Poplar Leaves.

Leaf osmotic adjustment by the active accrual of compatible organic solutes (e.g. sucrose) contributes to drought tolerance throughout the plant kingdom. In Populus tremula x alba, PtaSUT4 encodes a tonoplast sucrose-proton symporter, whose downregulation by chronic mild drought or transgenic manipulation is known to increase leaf sucrose and turgor. While this may constitute a single drought tolerance mechanism, we now report that other adjustments which can occur during a worsening water deficit are damped when PtaSUT4 is constitutively downregulated. Specifically, we report that starch use and leaf relative water content (RWC) dynamics were compromised when plants with constitutively downregulated PtaSUT4 were subjected to a water deficit. Leaf RWC decreased more in wild-type and vector control lines than in transgenic PtaSUT4-RNAi (RNA-interference) or CRISPR (clustered regularly interspersed short palindromic repeats) knockout (KO) lines. The control line RWC decrease was accompanied by increased PtaSUT4 transcript levels and a mobilization of sucrose from the mesophyll-enriched leaf lamina into the midvein. The findings suggest that changes in SUT4 expression can increase turgor or decrease RWC as different tolerance mechanisms to reduced water availability. Evidence is presented that PtaSUT4-mediated sucrose partitioning between the vacuole and the cytosol is important not only for overall sucrose abundance and turgor, but also for reactive oxygen species (ROS) and antioxidant dynamics. Interestingly, the reduced capacity for accelerated starch breakdown under worsening water-deficit conditions was correlated with reduced ROS in the RNAi and KO lines. A role for PtaSUT4 in the orchestration of ROS, antioxidant, starch utilization and RWC dynamics during water stress and its importance in trees especially, with their high hydraulic resistances, is considered.

The Dark Side of Development: A Systems Characterization of the Negative Mentoring Experiences of Doctoral Students.

Effective mentoring promotes the development and success of graduate students. Yet mentoring, like other relationships, can have negative elements. Little knowledge exists about the problematic mentoring that graduate students experience despite its potentially detrimental impacts. To begin to address this gap, we conducted an exploratory interview study to define and characterize negative mentoring experiences of 40 life science doctoral students. Students attributed their negative mentoring experiences to interacting factors at multiple levels-from interpersonal differences and poor relationship quality to issues at the research group, departmental, organizational, and discipline levels-all of which they perceived as harmful to their development. We found that doctoral students experienced forms of negative mentoring similar to those reported in workplace and undergraduate research settings, but they also experienced negative mentoring that was unique to academic research and their stage of development. Our results are useful to mentors for reflecting on ways their behaviors might be perceived, to mentees for avoiding situations that might be conducive to negative mentoring, and to programs and institutions for improving structures and processes to prevent negative mentoring. Our findings also serve as a foundation for future research on the prevalence and impacts of negative mentoring experiences in graduate education.

"Where's My Mentor?!" Characterizing Negative Mentoring Experiences in Undergraduate Life Science Research.

Undergraduate research experiences in science, technology, engineering, and mathematics fields are championed for promoting students' personal and professional development. Mentorship is an integral part of undergraduate research, as effective mentorship maximizes the benefits undergraduates realize from participating in research. Yet almost no research examines instances in which mentoring is less effective or even problematic, even though prior research on mentoring in workplace settings suggests negative mentoring experiences are common. Here, we report the results of a qualitative study to define and characterize negative mentoring experiences of undergraduate life science researchers. Undergraduate researchers in our study reported seven major ways they experienced negative mentoring: absenteeism, abuse of power, interpersonal mismatch, lack of career support, lack of psychosocial support, misaligned expectations, and unequal treatment. They described some of these experiences as the result of absence of positive mentoring behavior and others as actively harmful behavior, both of which they perceive as detrimental to their psychosocial and career development. Our results are useful to mentors for reflecting on ways their behaviors might be perceived as harmful or unhelpful. These findings can also serve as a foundation for future research aimed at examining the prevalence and impact of negative mentoring experiences in undergraduate research.