Boron (B) is an essential micronutrient for vascular plant growth. Both B deficiency and toxicity can impair tissue development in diverse plant species, but little is known about the effect of B on reproductive panicle development and grain yield. In this study, a mutant of Setaria italica exhibiting necrotic panicle apices was identified and designated as sibor1. Sequencing revealed a candidate gene, SiBOR1, with a G-to-A alteration at the seventh exon. Knockout transgenic lines generated by clustered regularly interspaced short palindromic repeats and their associated protein-9 also had necrotic panicles, verifying the function of SiBOR1. SiBOR1 encoded a membrane-localized B efflux transporter, co-orthologous to the rice BOR1 protein. SiBOR1 was dominantly expressed in panicles and displayed a distinct expression pattern from those of its orthologs in other species. The induced mutation in SiBOR1 caused a reduction in the B content of panicle primary branches, and B deficiency-associated phenotypes such as thicker cell walls and higher cell porosity compared with Yugu 1. Transcriptome analysis indicated that differentially expressed genes involved in cell wall biogenesis, jasmonic acid synthesis, and programmed cell death response pathways were enriched in sibor1. qPCR analysis identified several key genes, including phenylalanine ammonia-lyase (SiPAL) and jasmonate-ZIM-domain (SiJAZ) genes, responsive to B-deficient conditions. These results indicate that SiBOR1 helps to regulate panicle primary branch development to maintain grain yield in S. italica. Our findings shed light on molecular mechanisms underlying the relationship between B transport and plant development in S. italica.

To elucidate the mechanism by which intercropping proso millet (Panicum miliaceum L.) with mung bean (Vigna radiata L.) increases proso millet yield and to determine how this higher yield results from maximization of resources use efficiency, we designed and conducted four strip intercropping row arrangements, including two rows of proso millet alternating with two rows of mung bean (2P2M), four rows of proso millet alternating with two rows of mung bean (4P2M), four rows of proso millet alternating with four rows of mung bean (4P4M), two rows of proso millet alternating with four rows of mung bean (2P4M), sole proso millet (SP, control) and sole mung bean (SM, control) in Yulin, Shaanxi, China. Photosynthetically active radiation (PAR) in the canopy, radiation use efficiency (RUE), leaf photosynthetic characteristics, dry matter accumulation and allocation, and yield of proso millet were investigated. The results showed that the intercropping systems had higher PAR than the monoculture. Mean PAR intensities were increased by respectively 2.2%–23.4%, 19.8%–59.7%, and 61.2%–133.3% in the proso millet upper, middle and lower canopies compared with SP. The increase in PAR directly increased RUE, a result attributed mainly to the increase in photosynthetic capacity, including net photosynthetic rate and chlorophyll content. These responses resulted in increased dry matter allocation to plant organs. Yield of intercropped proso millet was 6.8%–37.3% higher than that under monoculture and the land equivalent ratios for the different intercropping patterns were all greater than unity (> 1). In general, yield followed a positive linear function of PAR in the intercropping system. The results indicated that intercropping can boost proso millet yield, evidently by altering light distribution within its canopy and consequently increasing RUE, thereby increasing leaf photosynthetic capacity, dry matter accumulation, and allocation to the grain. The optimum combination for improving the growth and yield of proso millet on the Loess Plateau of China was 2P4M.