CalS7 encodes a callose synthase responsible for callose deposition in the phloem

Abstract

SUMMARYIt has been known for more than a century that sieve plates in the phloem in plants contain callose, a b-1,3-glucan. However, the genes responsible for callose deposition in this subcellular location have not been identified. In this paper we examine callose deposition patterns in T-DNA insertion mutants (cs7) of the Callose Synthase 7 (CalS7) gene. We demonstrated here that the CalS7 gene is expressed specifically in the phloem of vascular tissues. Callose deposition in the phloem, especially in the sieve elements, was greatly reduced in cs7 mutants. Ultrastructural analysis of developing sieve elements revealed that callose failed to accumulate in the plasmodesmata of incipient sieve plates at the early perforation stage of phloem development, resulting in the formation of sieve plates with fewer pores. In wild-type Arabidopsis plants, callose is present as a constituent polysaccharide in the phloem of the stem, and its accumulation can also be induced by wounding. Callose accumulation in both conditions was eliminated in mature sieve plates of cs7 mutants. These results demonstrate that CalS7 is a phloem-specific callose synthase gene, and is responsible for callose deposition in developing sieve elements during phloem formation and in mature phloem induced by wounding. The mutant plants exhibited moderate reduction in seedling height and produced aberrant pollen grains and short siliques with aborted embryos, suggesting that CalS7 also plays a role in plant growth and reproduction.

Callose Synthase GSL7 Is Necessary for Normal Phloem Transport and Inflorescence Growth in Arabidopsis

“…Callose may influence both the effective length of the pore, by preventing wall thickening around the developing pore, and its flow characteristics, by providing a rigid lining and hence an invariant diameter under mass flow conditions. After acceptance of this paper, we became aware of another paper published online that also reports the importance of GSL7 for callose synthesis in the phloem (Xie et al, 2010). The authors propose that the loss of callose in gsl7 mutants hampers sieve plate pore formation, whereas our work indicates that pore function rather than pore formation is hampered.…”

The Coiled-Coil and Nucleotide Binding Domains of BROWN PLANTHOPPER RESISTANCE14 Function in Signaling and Resistance against Planthopper in Rice

“…Several RLCKs are thought to play pivotal roles in plant defense (Martin et al, 1994;Swiderski and Innes, 2001;Zhang et al, 2010;Shi et al, 2013;Liu et al, 2011;Feng et al, 2012;Shinya et al, 2014;Yamaguchi et al, 2013;Dubouzet et al, 2011;Wang et al, 2015b;Zhou et al, 2016) and are thought to be involved in connecting signal perception by RLKs in the plasma membrane to downstream intracellular signal transduction systems. Callose synthases such as LOC_Os01g67364.1 perform callose biosynthesis in plants (Xie et al, 2011), and there is considerable evidence that they function in preventing penetration by herbivores (Enrique et al, 2011;Blümke et al, 2013Blümke et al, , 2014Ellinger et al, 2013). We found that the promoters of RLCK281 and LOC_Os01g67364.1 were associated with WRKY46 and WRKY72; the presence of the CC, NB, and CN domains or FL BPH14 enhanced the association between the WRKYs and the promoters of RLCK281 and LOC_Os01g67364.1 in rice.…”

CHOLINE TRANSPORTER-LIKE1 is required for sieve plate development to mediate long-distance cell-to-cell communication

“…1b). Callose deposition around plasmodesmata has been suggested to have an important role in initiating this process 23 .…”

“…Callose has been shown to be involved in the regulation of the sieve pore diameter. In cals7 mutants reduced callose deposition at the sieve plate leads to a reduced number of open pores per sieve plate, smaller diameter sieve pores and impaired phloem transport 22,23 . But also over accumulation of callose, as shown by the phloem-specific expression of a gain of function mutant of CalS3, inhibits phloem conductivity 24 , suggesting that callose deposition at the sieve plate has to be tightly regulated.…”