Indole-3-acetic acid levels and gene copy number in the indirect somatic embryogenesis of diploid and allotetraploid Coffea

Coffea indirect somatic embryogenesis (ISE) has been established from callogenesis heading towards somatic embryo regeneration, evidencing intra- and interspecific similarities and differences between diploid (Coffea canephora and Coffea eugenioides) and allotetraploid (Coffea arabica). ISE is influenced by endogenous and exogenous aspects, but few data have been reported about the genetic and physiological causes. Seeking to understand the Coffea ISE responses, we aimed to: induce ISE in diploid and allotetraploid, quantify the endogenous levels of indole-3-acetic acid (IAA), and determine the gene copy number of aux/iaa33 and yuc4 involved in auxin biosynthesis, and of wox4 related with ISE pathway. Unlike previous studies, C. eugenioides and C. arabica showed the same friable callus mean number, and higher mean number than C. canephora. Nevertheless, C. canephora friable calli had higher IAA level at 60th than other Coffea. IAA level of the C. canephora friable calli reduced at 90th, becoming equal to C. eugenioides and C. arabica even the diploid Coffea exhibiting one copy and allotetraploid two copies of the aux/iaa33, yuc4 and wox4. As in other studies, C. arabica exhibited a higher somatic embryo mean number than diploid Coffea. Since the ISE was established in the same conditions, our data reinforce the endogenous IAA role in Coffea ISE, and that the aux/iaa33, yuc4 and wox4 copy number did not affect IAA levels. Therefore, other genes, genotype and hormones should be further investigated. Our data are a basis for understanding the in vitro response and contribute to ISE improvement.