UNBRANCHED3 regulates branching by modulating cytokinin biosynthesis and signaling in maize and rice

Abstract

UNBRANCHED3 (UB3), a member of the SQUAMOSA promoter binding protein-like (SPL) gene family, regulates kernel row number by negatively modulating the size of the inflorescence meristem in maize. However, the regulatory pathway by which UB3 mediates branching remains unknown. We introduced the UB3 into rice and maize to reveal its effects in the two crop plants, respectively. Furthermore, we performed transcriptome sequencing and protein-DNA binding assay to elucidate the regulatory pathway of UB3. We found that UB3 could bind and regulate the promoters of LONELY GUY1 (LOG1) and Type-A response regulators (ARRs), which participate in cytokinin biosynthesis and signaling. Overexpression of exogenous UB3 in rice (Oryza sativa) dramatically suppressed tillering and panicle branching as a result of a greater decrease in the amount of active cytokinin. By contrast, moderate expression of UB3 suppressed tillering slightly, but promoted panicle branching by cooperating with SPL genes, resulting in a higher grain number per panicle in rice. In maize (Zea mays) ub3 mutant with an increased kernel row number, UB3 showed a low expression but cytokinin biosynthesis-related genes were up-regulated and degradation-related genes were down-regulated. These results suggest that UB3 regulates vegetative and reproductive branching by modulating cytokinin biosynthesis and signaling in maize and rice.

Genetic improvement of the shoot architecture and yield in soya bean plants via the manipulation of GmmiR156b

“…Therefore, an optimal balance between apical growth and branching is critical to achieve an IPA and high yields. In rice and other plants, overexpression of GmmiR156 results in increased tillers but stunted plants (Liu et al, 2017;Wang et al, 2015a). By contrast, GmmiR156b overexpression did not affect the activity of the soya bean apical meristem and primary shoot growth (Figures 1a,d and 3a).…”

“…Arabidopsis and alfalfa). Overexpression of miR156 increases branching, resulting in bushy plants (Chuck et al, 2007;Fu et al, 2012;Liu et al, 2017;Luo et al, 2012;Schwab et al, 2005;Xie et al, 2012). In monocots, tiller number is related to the number of spikes or panicles per plant.…”

“…In monocots, tiller number is related to the number of spikes or panicles per plant. The fact that miR156 overexpression causes an increase in tiller number and reduction in spike number (Liu et al, 2017;Wang et al, 2015a,b) has hindered the application of miR156 in IPA breeding. In soya bean, branch number is directly correlated with the pod number per plant, and long branches with effective nodes are a key requirement for the first ISA model.…”

“…Since then, their effects on plant architecture have been recognized in various species, including Arabidopsis and rice (Aung et al, 2014;Schwarz et al, 2008;Wang et al, 2015b). MiR156s affect shoot branching and plant architecture by cleaving SPL transcripts (Du et al, 2017;Liu et al, 2017;Wang et al, 2015b). Overexpression of miR156s promotes axillary bud initiation and outgrowth while suppressing SAM activity, causing a dwarf plant phenotype (Schwarz et al, 2008;Wang et al, 2015a).…”

Sorghum tiller bud growth is repressed by contact with the overlying leaf

“…Tiller development is analogous to branch development in eudicots and shares many similarities. For instance, axillary buds in both programs are suppressed by a low ratio of red light to far‐red light (R:FR; Finlayson, Krishnareddy, Kebrom, & Casal, ; Kebrom, Burson, & Finlayson, ), are promoted by photosynthate (Kebrom & Mullet, ; Mason, Ross, Babst, Wienclaw, & Beveridge, ), are promoted by cytokinins (Du et al, ; Muller et al, ), are inhibited by strigolactones (Janssen, Drummond, & Snowden, ), are inhibited by auxin (Stirnberg, Chatfield, & Leyser, ; Zhang et al, ), and share homologous TCP domain family regulators that suppress outgrowth (Aguilar‐Martínez, Poza‐Carrión, & Cubas, ; Doebley, Stec, & Hubbard, ).…”