The miR156‐SPL4 module predominantly regulates aerial axillary bud formation and controls shoot architecture

Abstract

Grasses possess basal and aerial axillary buds. Previous studies have largely focused on basal bud (tiller) formation but scarcely touched on aerial buds, which may lead to aerial branch development. Genotypes with and without aerial buds were identified in switchgrass (Panicum virgatum), a dedicated bioenergy crop. Bud development was characterized using scanning electron microscopy. Microarray, RNA-seq and quantitative reverse transcription polymerase chain reaction (RT-qPCR) were used to identify regulators of bud formation. Gene function was characterized by down-regulation and overexpression. Overexpression of miR156 induced aerial bud formation in switchgrass. Various analyses revealed that SQUAMOSA PROMOTER BINDING PROTEIN LIKE4 (SPL4), one of the miR156 targets, directly regulated aerial axillary bud initiation. Down-regulation of SPL4 promoted aerial bud formation and increased basal buds, while overexpression of SPL4 seriously suppressed bud formation and tillering. RNA-seq and RT-qPCR identified potential downstream genes of SPL4. Unlike all previously reported genes acting as activators of basal bud initiation, SPL4 acts as a suppressor for the formation of both aerial and basal buds. The miR156-SPL4 module predominantly regulates aerial bud initiation and partially controls basal bud formation. Genetic manipulation of SPL4 led to altered plant architecture with increased branching, enhanced regrowth after cutting and improved biomass yield.

Genome-wide analysis of structures and characteristics of the SPL gene family in wheat (Triticum aestivum L.)

“…As negative regulators, miRNAs could repress target gene expression through post-transcriptional degradation and translational repression and play indispensable roles in diverse stress responses [42,43]. MicroRNA156, as previously reported, was involved in a variety signalling pathways by inhibiting SPL gene family members [16,19,23,36,44]. In Arabidopsis, 11 of 17 SPL genes were predicted to be miR156/miR157 targets [23].…”

“…However, these SPL genes showed signi cant difference in gene size and structure, so that there are signi cant differences in their functions. Previous studies have shown that SPL genes exhibit functional diversity in different plant species, including shoot architecture [15], axillary bud formation [16], plant architecture [17][18][19][20], male fertility [21], owering regulation [7,[22][23][24][25], in orescence branching [24,26], organ size [27][28][29][30] and grain yield [17,27]. In Arabidopsis, AtSPL3 has been rst identi ed gene and involved in the oral transition [7].…”

“…MiRNA156-targeted SPL13 increased drought stress tolerance in alfalfa (Medicago sativa L.) [40]. Interesting, the functions of partial SPL genes were regulated by miRNA156 [16,23,35,36].…”

SPL7 and SPL8 represent a novel flowering regulation mechanism in switchgrass

“…By contrast to the extensive studies in Arabidopsis , little information is available regarding the roles of SPLs related to flowering in grasses. To date, only a few SPL s have been investigated in the regulation of the other development processes in grasses, including grain size and shape in rice (Wang et al ., 2015b; Si et al ., ), panicle branching in rice (Jiao et al ., ; Miura et al ., ) and axillary bud formation in switchgrass (Gou et al ., ). In the present study, we demonstrated that SPL7 and SPL8 redundantly regulated flowering in switchgrass.…”

“…Shoot apical meristem (SAM) or inflorescence samples were harvested and immediately fixed in 3% glutaraldehyde (in 25 mM phosphate buffer, pH 7.0) overnight and dehydrated in a graded ethanol series. The fixed, dried and sputter‐coated samples were observed by using scanning electron microscopy (SEM) as reported previously (Gou et al ., ).…”