BRI1 Signaling in the Root is Mediated through the SERK1 and SERK3 Co-receptors

Brassinosteroid (BR) is a class of polyhydroxysteroids plant hormones known to regulate shoot and root growth. Genetic and molecular analyses demonstrate that receptor kinase BRI1 protein acts as a perceiver for BR. One of the characteristics of bri1 mutant’s phenotypes is the complete BR insensitivity in the root. Biochemical evidences of the BRI1 protein complex indicates that somatic embryogenesis receptor kinase 1 (SERK1) and SERK3 participate in the BR pathway in Arabidopsis root. While only serk3 mutants show partial reduction to BR sensitivity, serk1 presents a normal BR penetration phenotype compared to the wild type. Interestingly, the double mutant serk1serk3 displays more, but not full resistance to BR in root length assay. In this study, we aimed to enhance the BR insensitivity of the double mutant serk1serk3 by crossing serk1 mutant allele with a strong serk3 and bri1 mutant alleles. In our study, by generating serk1-3serk3-2 double mutants, a complete insensitivity to BR that phenocopied bri1-301 mutant was recorded. However, we were unable to increase BR resistance in the root of serk1-3serk3-2 double mutant by crossing with bri1 mutant allele in the triple mutant serk1-3serk3-2bri1. As a result, all the BRI1 signaling in the root was mediated through the SERK1 and SERK3 co-receptors. Additionally, we established that based on conventional BR assays, the At1g27190 protein was also involved in BR signaling. Preliminary data indicated that the triple mutant serk1serk3-2At1g27190 showed a dwarfed phenotype. Whether or not this dwarfed phenotype is linked to BRI1 signaling impairment needs to be further investigated.

Agrobacterium-mediated transformation of the wild orchid Cattleya maxima Lindl

Protocorms are unique anatomical structures; they are akin to rhizoids and are formed by young orchid seedlings under physiological conditions. Explanted orchid tissues produce similar structures called protocorm-like bodies (PLBs) when exposed to appropriate <em>in vitro</em> growing conditions. Both the propagative nature of PLBs and the easiness by which they can be generated, make these structures an attractive alternative to seed-mediated production for growing large numbers of plants. To increase somatic embryogenesis and optimize the procedure, PLBs of <em>Cattleya maxima </em>were transformed<em> </em>using the <em>Agrobacterium tumefaciens </em>method. The T-DNA carried a Hygromycin-resistance gene, a visible marker (GFP5-GUSA) and a rice gene encoding the Somatic Embryogenesis Receptor Kinase, deemed to be important for somatic embryogenesis. Treated PLBs generated somatic embryos developing Hygromycin-resistant plantlets. The insertion of T-DNA was confirmed by PCR, and GFP expression was observed using a fluorescent stereomicroscope. Transformed <em>Cattleya maxima</em> PLBs were more efficient in forming somatic embryos (60-80%) than untransformed controls (45-57%), and this contrast was maximized in hormone-free, Murashige and Skoog (MS) medium (80% of the transformed plants compared to 57% of the untransformed ones). This finding supports the notion that SERK<em> </em>plays an important role in Orchid embryogenesis.

Identification of Serk Gene from Bract Derived Embryogenic and Non - Embryogenic Calli of Four Diploid Banana Cultivars from South India

Somatic embryogenesis receptor kinase (SERK) gene is known to be a marker of somatic embryogenesis in several plant species. The present study reported the presence of SERK gene from bract derived embryogenic calli bearing somatic embryos. The analysis of the expression pattern of the SERK gene during embryogenic cell formation and somatic embryogenesis revealed that SERK expression continued during pro embryogenic mass formation. In the present study the amplified product of cDNA from the somatic embryos has molecular size 1459 bp. The non- embryogenic callus also showed the presence of faint bands. In all the samples the amplified product from β - actin primer showed bands of 650 bp with similar intensity in both the embryogenic and non- embryogenic samples.