Madison Plunkert

A bstract: Extrafloral nectaries (EFNs) are a widespread plant defense mutualism trait and are highly convergent, appearing in hundreds of plant lineages worldwide. Here we investigate a report of possible EFNs in Erythranthe angulosa , a recently-described California wildflower. We integrate field observations, insect bioassays, an induction experiment, and microscopy to test for signatures of EFN function, finding no evidence that the distinctive axillary swellings produced by E. angulosa function as EFNs. We also uncovered two distinct morphs at the type locality of E. angulosa that diverge in the number of axillary swellings produced, as well as other shoot architecture traits such as stem thickness, leaf size, and branch number. Although the axillary swellings appear to not function as EFNs, they remain a compelling morphological variant within the yellow monkeyflowers that may perform storage or another unknown function.

Premise: Surviving the effects of oceanic salt spray is critical for plants in coastal ecosystems, yet the mechanisms of coastal plant resilience to salt spray are not well understood. We investigated mechanisms of salt spray adaptation by comparing five latitudinal pairs of yellow monkeyflower accessions locally adapted to coastal and inland habitats. Methods: We measured sodium levels in coastal and inland leaves exposed to experimental salt spray in the laboratory and compared leaf surface traits that may contribute to differences in sodium uptake between ecotypes. We assayed tissue tolerance by allowing sodium to enter leaf discs through the cut edges and recording time to necrosis for coastal and inland accessions. Results: The leaf surface of coastal accessions took up less sodium from the experimental salt spray than the inland accessions, which may contribute to local adaptation to oceanic salt spray in coastal habitats. Higher water content per unit leaf area and less water loss under salt spray further reduced sodium concentrations in salt‐sprayed coastal leaves compared to inland accessions. The coastal ecotype also had greater tissue tolerance to sodium than the inland ecotype. Conclusions: Coastal monkeyflowers employ salt spray exclusion and tissue tolerance mechanisms for salt spray resilience. Our results suggest that plant adaptation to coastal habitats may often involve the evolution of multiple mechanisms to survive stress imposed by oceanic salt spray.

The evolutionary mechanisms leading to nonfunctional trait loss are not well understood. Some Arabidopsis thaliana populations display incomplete loss of short stamens, floral organs that do not contribute significantly to seed set in this species. In nature, short stamen number is correlated with ovule number and flowering time, suggesting that tight linkage or pleiotropy with these traits could drive stamen number evolution. To investigate the role of colocalized QTLs in short stamen number evolution and the repeatability of QTL co-localization between replicate mapping populations, we performed QTL mapping of stamen number, ovule number, and flowering time for two sets of recombinant inbred lines (RILs), Belm-12 x Roda-47 and Tsu-1 x Kas-1. All three traits were correlated in Belm-12 x Roda-47 RILs, but none were correlated in Tsu-1 x Kas-1 RILs. For both stamen and ovule number, some QTLs were unique to each RIL set and others were shared. Notably, for Belm-12 x Roda-47 RILs, we mapped QTLs affecting ovule and short stamen number to a region of chromosome 5 that also affects flowering time. For Tsu-1 x Kas-1 RILs, we identified the same chromosome 5 region as a short stamen number QTL, but ovule number and flowering time QTLs map to other genomic regions. Tests for pleiotropy revealed that the flowering time and short stamen number QTLs on chromosome 5 in Belm-12 x Roda-47 are likely separate QTLs, linked but not pleiotropic, but each may have pleiotropic effects on ovule number. Thus, the large-effect stamen number QTL on chromosome 5 was consistent between crosses, but only in Belm-12 x Roda-47 does this QTL co-localize with the other two traits. Article summary: Nonfunctional trait loss is common over evolutionary time. We investigated the evolutionary mechanisms influencing nonfunctional trait loss by examining the genetic architecture of short stamen number, which has limited effects on seed set in the highly selfing plant Arabidopsis thaliana . We used QTL mapping to find loci affecting stamen number and other reproductive traits correlated with stamen number in nature. The same genomic region affected stamen number and other reproductive traits in one of our two replicate mapping populations, but not the other. The patterns of QTL co-localization are thus cross-specific.

Premise: Surviving under oceanic salt spray is critical for plants in coastal ecosystems, yet the mechanisms of coastal plant resilience to salt spray are not well understood. We investigated mechanisms of salt spray adaptation by comparing five latitudinal pairs of yellow monkeyflower accessions locally adapted to coastal and inland habitats. Methods: We measured sodium levels in coastal and inland leaves exposed to experimental salt spray in the lab, and compared leaf surface traits that may contribute to differences in sodium uptake between ecotypes. We assayed tissue tolerance by allowing sodium to enter leaves through wounding and recording time to necrosis for coastal and inland accessions. Key Results: Coastal monkeyflowers take up less sodium through the leaf surface under experimental salt spray, which may contribute to local adaptation under oceanic salt spray in coastal habitats. Higher water content per unit leaf area and less water loss under salt spray further reduce sodium concentrations in salt-sprayed coastal leaves compared to inland counterparts. The coastal ecotype also shows greater tissue tolerance to sodium than the inland ecotype. Conclusions: Coastal monkeyflowers employ salt spray exclusion and tissue tolerance mechanisms for salt spray resilience. Our results suggest that plant adaptation to coastal habitats may often involve the evolution of multiple mechanisms to survive stress imposed by oceanic salt spray.

The R2R3-MYB transcription factor FveMYB10 is a major regulator of anthocyanin pigmentation in the red strawberry fruits. fvemyb10 loss-of-function mutants form yellow fruits but still accumulate purple-colored anthocyanins in the petioles, suggesting that anthocyanin biosynthesis is under distinct regulation in fruits and petioles. We identified a green petioles (gp)-1 mutant from chemical mutagenesis in the diploid wild strawberry Fragaria vesca that lacks anthocyanins in petioles. Using mapping-by-sequencing and transient functional assays, we confirmed that the causative mutation resides in a FveMYB10-Like (MYB10L) gene and that FveMYB10 and FveMYB10L function independently in the fruit and petiole respectively. In addition to their tissue-specific regulation, FveMYB10 and FveMYB10L respond differently to changes in light quality, produce distinct anthocyanin compositions, and preferentially activate different downstream anthocyanin biosynthesis genes in their respective tissues. This work identifies a new regulator of anthocyanin synthesis and demonstrates that two paralogous MYB genes with specialized functions enable tissue-specific regulation of anthocyanin biosynthesis in fruit and petiole tissues.

Summary: Leaves are strikingly diverse in terms of shapes and complexity. The wild and cultivated strawberry plants mostly develop trifoliate compound leaves, yet the underlying genetic basis remains unclear in this important fruit crop in Rosaceae. Here, we identified two EMS mutants designated simple leaf1 (sl1‐1 and sl1‐2) and one natural simple‐leafed mutant monophylla in Fragaria vesca. Their causative mutations all reside in SL1 (FvH4_7g28640) causing premature stop codon at different positions in sl1‐1 and sl1‐2 and an eight‐nucleotide insertion (GTTCATCA) in monophylla. SL1 encodes a transcription regulator with the conserved DNA‐binding domain GT‐1 and the catalytic domain of protein kinases PKc. Expression of SL1pro::SL1 in sl1‐1 completely restored compound leaf formation. The 35S::SL1 lines developed palmate‐like leaves with four or five leaflets at a low penetrance. However, overexpressing the truncated SL1^ΔPK caused no phenotypes, probably due to the disruption of homodimerization. SL1 is preferentially expressed at the tips of leaflets and serrations. Moreover, SL1 is closely associated with the auxin pathway and works synergistically with FveLFYa in leaf morphogenesis. Overall, our work uncovered a new type of transcription regulator that promotes compound leaf formation in the woodland strawberry and shed new lights on the diversity of leaf complexity control.

The dominance of flowering plants on earth is owed largely to the evolution of maternal tissues such as fruit and seedcoat that protect and disseminate the seeds. The mechanism of how fertilization triggers the development of these specialized maternal tissues is not well understood. A key event is the induction of auxin synthesis in the endosperm, and the mobile auxin subsequently stimulates seedcoat and fruit development. However, the regulatory mechanism of auxin synthesis in the endosperm remains unknown. Here, we show that a type I MADS box gene AGL62 is required for the activation of auxin synthesis in the endosperm in both Fragaria vesca, a diploid strawberry, and in Arabidopsis. Several strawberry FveATHB genes were identified as downstream targets of FveAGL62 and act to repress auxin biosynthesis. In this work, we identify a key mechanism for auxin induction to mediate fertilization success, a finding broadly relevant to flowering plants.