Heat stress leads to rapid lipid remodeling and transcriptional adaptations in Nicotiana tabacum pollen tubes

Abstract

After reaching the stigma, pollen grains germinate and form a pollen tube that transports the sperm cells to the ovule. Due to selection pressure between pollen tubes, pollen grains likely evolved mechanisms to quickly adapt to temperature changes to sustain elongation at the highest possible rate. We investigated these adaptions in tobacco (Nicotiana tabacum) pollen tubes grown in vitro under 22 °C and 37 °C by a multi-omics approach including lipidomic, metabolomic, and transcriptomic analysis. Both glycerophospholipids and galactoglycerolipids increased in saturated acyl chains under heat stress, while triacylglycerols changed less in respect to desaturation but increased in abundance. Free sterol composition was altered, and sterol ester levels decreased. The levels of sterylglycosides and several sphingolipid classes and species were augmented. Most amino acid levels increased during heat stress, including the non-codogenic amino acids γ-amino butyrate and pipecolate. Furthermore, the sugars sedoheptulose and sucrose showed higher levels. Also, the transcriptome underwent pronounced changes with 1,570 of 24,013 genes being differentially upregulated and 813 being downregulated. Transcripts coding for heat shock proteins and many transcriptional regulators were most strongly upregulated but also transcripts that have so far not been linked to heat stress. Transcripts involved in triacylglycerol synthesis increased, while the modulation of acyl chain desaturation seemed not to be transcriptionally controlled, indicating other means of regulation. In conclusion, we show that tobacco pollen tubes are able to rapidly remodel their lipidome under heat stress likely by post-transcriptional and/or post-translational regulation.

Comprehensive analysis of glycerolipid dynamics during tobacco pollen germination and pollen tube growth

“…Paradoxically, this is often the case when pollen tubes are separated from the medium without great care prior to hot isopropanol treatment. Seeming PA levels in whole cell samples may reach 20-60% of total glycerolipids, as was reported for soybean, tobacco, or Arabidopsis pollen (Djanaguiraman et al, 2013;McDowell et al, 2013;Krawczyk et al, 2022). Our data, reporting whole cell PA levels at 1.5-2.3% of total glycerolipids and PA levels in the PM at ~7% of total glycerolipids, agree with the data on wheat pollen and purified plasma membrane from tobacco cell culture (Cacas et al, 2016;Narayanan et al, 2018).…”

“…Conversely, PS molecular species show distinct trends in both acyl-chain composition and relative changes during pollen germination and growth, which are unapparelled with other tested glycerolipids ( Figure 3 ). First, predominant PS species PS 40:2, PS 40:3, PS 42:2, and PS 42:3, containing very-long-chain fatty acids (VLCFAs), together constitute >90% of total pollen PS, which contrasts with reported values for Arabidopsis ( McDowell et al., 2013 ), wheat ( Narayanan et al., 2018 ) and tobacco ( Krawczyk et al., 2022 ) pollen. Second, PS species show unique dual dynamics, where particularly shorter species (PS 34:3 and 34:2) are significantly upregulated in the pollen tube phase.…”

“…Despite the apparent importance of membrane lipids in tip-growing pollen tubes, high-throughput lipidomic analyses in pollen are scarce compared to the wealth of data from sporophytic tissues. To some extent, pollen glycerolipids had been analyzed in rape seed ( Piffanelli et al., 1997 ), lily ( Nakamura et al., 2009 ), Arabidopsis ( McDowell et al., 2013 ), wheat ( Narayanan et al., 2018 ), tobacco ( Krawczyk et al., 2022 ), and olive ( Hernández et al., 2020 ). However, most of these studies studied non-germinated pollen grains or focused on pollen responses to heat stress.…”

Environmental gradients reveal stress hubs predating plant terrestrialization

“…In land plants lipid droplet (LD) formation and TAG accumulation is common to many stress responses, including heat, cold and drought (Higashi et al, 2015; Mueller et al, 2015; Gidda et al, 2016; Doner et al, 2021; Krawczyk et al, 2022). We observed that cells of Mesotaenium accumulated inclusions resembling LDs (Figure 6a) upon prolonged exposure to stress.…”

Pollen performance of pomegranate under high-temperature stress

“…It has been known that low or high temperature mostly have opposite impacts on PP (Krawczyk et al, 2022). For instance; PG and PT length were decreased by hightemperature treatment at 30 °C in hazelnut (Çetinbaş-Genç et al, 2019) and, decreased by high-temperature treatment above 35 °C in cotton and tobacco (Song et al, 2015;Parrotta et al, 2016).…”