From model to crop: functional characterization of SPL8 in M. truncatula led to genetic improvement of biomass yield and abiotic stress tolerance in alfalfa

Abstract

SummaryBiomass yield, salt tolerance and drought tolerance are important targets for alfalfa (Medicago sativa L.) improvement. Medicago truncatula has been developed into a model plant for alfalfa and other legumes. By screening a Tnt1 retrotransposon‐tagged M. truncatula mutant population, we identified three mutants with enhanced branching. Branch development determines shoot architecture which affects important plant functions such as light acquisition, resource use and ultimately impacts biomass production. Molecular analyses revealed that the mutations were caused by Tnt1 insertions in the SQUAMOSA PROMOTER BINDING PROTEIN‐LIKE 8 (SPL8) gene. The M. truncatula spl8 mutants had increased biomass yield, while overexpression of SPL8 in M. truncatula suppressed branching and reduced biomass yield. Scanning electron microscopy (SEM) analysis showed that SPL8 inhibited branching by directly suppressing axillary bud formation. Based on the M. truncatula SPL8 sequence, alfalfa SPL8 (MsSPL8) was cloned and transgenic alfalfa plants were produced. MsSPL8 down‐regulated or up‐regulated alfalfa plants exhibited similar phenotypes to the M. truncatula mutants or overexpression lines, respectively. Specifically, the MsSPL8 down‐regulated alfalfa plants showed up to 43% increase in biomass yield in the first harvest. The impact was even more prominent in the second harvest, with up to 86% increase in biomass production compared to the control. Furthermore, down‐regulation of MsSPL8 led to enhanced salt and drought tolerance in transgenic alfalfa. Results from this research offer a valuable approach to simultaneously improve biomass production and abiotic stress tolerance in legumes.

Engineering abiotic stress response in plants for biomass production

“…Earlier studies demonstrated that down-regulation of SPL8 (Squamosa Promoter-binding-Like protein-8) transcription factor significantly increased branching by promoting axillary bud development and enhanced forage biomass yield, besides enhancing salt and drought tolerance in alfalfa (66); these transgenic plants showed reduced GA accumulation, while spl8 mutants showed significantly higher GA transcript abundance. Furthermore, GA2-ox6, which is the prime GA deactivation enzyme, is significantly up-regulated by SPL8 (66). These results suggest that SPL8 regulates GA signaling, and GA2-ox is a possible key node of this signaling network (67).…”

SPL7 and SPL8 represent a novel flowering regulation mechanism in switchgrass

“…Total RNA samples from biological replicates of the selected transgenic events and the control were extracted from SAMs at the R 0 stage using Spectrum™ Plant Total RNA Kit (Sigma‐Aldrich). Microarray hybridization, data collection and analyses follow the procedures reported previously (Gou et al ., ).…”

Transcriptome and Small RNA Sequencing Analysis Revealed Roles of PaWB-Related miRNAs and Genes in Paulownia fortunei

“…In this work, six DERs that may be related to plant defense or morphogenesis were selected to construct the miRNA-target gene interaction network based on gene function annotation. Previous studies demonstrated that downregulation of squamosa promoter binding protein-like 8 (SPL8) could increase branch development by facilitating the formation of axillary buds [53] and regulate the GA signaling pathway and biosynthesis in stem elongation [54]. Gou et al [53] indicated that GA signaling transduction was regulated by SPL8 from the upstream GA receptor (GID1) to the downstream responsive genes (GRASs).…”

“…Previous studies demonstrated that downregulation of squamosa promoter binding protein-like 8 (SPL8) could increase branch development by facilitating the formation of axillary buds [53] and regulate the GA signaling pathway and biosynthesis in stem elongation [54]. Gou et al [53] indicated that GA signaling transduction was regulated by SPL8 from the upstream GA receptor (GID1) to the downstream responsive genes (GRASs). GID1 sensed and bound endogenous GA to induce the formation of GID1-GA-DELLA protein complex [53].…”

“…Gou et al [53] indicated that GA signaling transduction was regulated by SPL8 from the upstream GA receptor (GID1) to the downstream responsive genes (GRASs). GID1 sensed and bound endogenous GA to induce the formation of GID1-GA-DELLA protein complex [53]. There was increasing evidence that the GA-GID1 complex caused rapid degradation of the DELLA protein [55] and DELLA as a nuclear transcription regulator could inhibit GA signaling and restrict plant growth [56].…”